# Try Manual

###### \[in package TRY\]
## The try ASDF System

- Version: 0.0.1
- Description: Try is an extensible test framework with equal support
  for interactive and non-interactive workflows.
- Long Description: Try stays as close to normal Lisp evaluation
  rules as possible. Tests are functions that record the checks they
  perform as events. These events provide the means of customization
  of what to debug, print, rerun. There is a single fundamental check,
  the extensible IS macro. Everything else is built on top.
- Licence: MIT, see COPYING.
- Author: Gábor Melis
- Mailto: [mega@retes.hu](mailto:mega@retes.hu)
- Homepage: [http://melisgl.github.io/try](http://melisgl.github.io/try)
- Bug tracker: [https://github.com/melisgl/try/issues](https://github.com/melisgl/try/issues)
- Source control: [GIT](https://github.com/melisgl/try.git)

## Links

Here is the [official repository](https://github.com/melisgl/try)
and the [HTML
documentation](http://melisgl.github.io/mgl-pax-world/try-manual.html)
for the latest version.

## Tutorial

Try is a library for unit testing with equal support for
interactive and non-interactive workflows. Tests are functions, and
almost everything else is a condition, whose types feature
prominently in parameterization.

Try is is what we get if we make tests functions and build a test
framework on top of the condition system as
[Stefil](https://common-lisp.net/project/stefil/index-old.shtml) did
but also address the issue of rerunning and replaying, make the
IS check more capable, use the types of the condition hierarchy
to parameterize what to debug, print, rerun, and finally document
the whole thing.

##### Looking for Truth

@TRY/IS is a replacement for CL:ASSERT, that can capture values of
subforms to provide context to failures:

```common-lisp
(is (= (1+ 5) 0))
.. debugger invoked on UNEXPECTED-RESULT-FAILURE:
..   UNEXPECTED-FAILURE in check:
..     (IS (= #1=(1+ 5) 0))
..   where
..     #1# = 6
```

This is a PAX transcript,
output is prefixed with `..`. Readable and unreadable return values
are prefixed with `=>` and `==>`, respectively.

Note the `#N#` syntax due to *PRINT-CIRCLE*.

##### Checking Multiple Values

IS automatically captures values of
arguments to functions like `1+` in the above example. Values of
other interesting subforms can be explicitly
captured. IS supports capturing multiple
values and can be taught how to deal with macros. The combination of these
features allows MATCH-VALUES to be implementable as tiny extension:

```common-lisp
(is (match-values (values (1+ 5) "sdf")
      (= * 0)
      (string= * "sdf")))
.. debugger invoked on UNEXPECTED-RESULT-FAILURE:
..   UNEXPECTED-FAILURE in check:
..     (IS
..      (MATCH-VALUES #1=(VALUES (1+ 5) #2="sdf")
..        (= * 0)
..        (STRING= * "sdf")))
..   where
..     #1# == 6
..            #2#
```

In the body of MATCH-VALUES, `*` is bound to
successive return values of some form, here `(VALUES (1+ 5) "sdf")`.
MATCH-VALUES comes with an automatic rewrite rule that captures the
values of this form, which are printed above as `#1# == 6 #2#`. IS
is flexible enough that all other checks (SIGNALS, SIGNALS-NOT,
INVOKES-DEBUGGER, INVOKES-DEBUGGER-NOT, FAILS, and IN-TIME are built
on top of it.

##### Writing Tests

Beyond IS, a fancy ASSERT, Try provides tests, which are Lisp
functions that record their execution in TRIAL objects. Let's define
a test and run it:

```common-lisp
(deftest should-work ()
  (is t))

(should-work)
.. SHOULD-WORK            ; TRIAL-START
..   ⋅ (IS T)             ; EXPECTED-RESULT-SUCCESS
.. ⋅ SHOULD-WORK ⋅1       ; EXPECTED-VERDICT-SUCCESS
..
==> #<TRIAL (SHOULD-WORK) EXPECTED-SUCCESS 0.000s ⋅1>
```

Try is driven by conditions, and the comments to the right give the
type of the condition that is printed on that line. The `⋅`
character marks successes.

We could have run our test with `(TRY 'SHOULD-WORK)` as well, which
does pretty much the same thing except it defaults to never entering
the debugger, whereas calling a test function directly enters the
debugger on events whose type matches the type in the variable
*DEBUG*.

```common-lisp
(try 'should-work)
.. SHOULD-WORK
..   ⋅ (IS T)
.. ⋅ SHOULD-WORK ⋅1
..
==> #<TRIAL (SHOULD-WORK) EXPECTED-SUCCESS 0.000s ⋅1>
```

##### Test Suites

Test suites are just tests that call other tests.

```common-lisp
(deftest my-suite ()
  (should-work)
  (is (= (foo) 5)))

(defun foo ()
  4)

(try 'my-suite)
.. MY-SUITE                 ; TRIAL-START
..   SHOULD-WORK            ; TRIAL-START
..     ⋅ (IS T)             ; EXPECTED-RESULT-SUCCESS
..   ⋅ SHOULD-WORK ⋅1       ; EXPECTED-VERDICT-SUCCESS
..   ⊠ (IS (= #1=(FOO) 5))  ; UNEXPECTED-RESULT-FAILURE
..     where
..       #1# = 4
.. ⊠ MY-SUITE ⊠1 ⋅1         ; UNEXPECTED-VERDICT-FAILURE
..
==> #<TRIAL (MY-SUITE) UNEXPECTED-FAILURE 0.000s ⊠1 ⋅1>
```

`⊠` marks UNEXPECTED-FAILUREs. Note how the failure of `(IS (= (FOO)
5))` caused `MY-SUITE` to fail as well. Finally, the `⊠1` and the
`⋅1` in the TRIAL's printed representation are the event
counts.

##### Filtering Output

To focus on the important bits, we can print only the UNEXPECTED
events:

```common-lisp
(try 'my-suite :print 'unexpected)
.. MY-SUITE
..   ⊠ (IS (= #1=(FOO) 5))
..     where
..       #1# = 4
.. ⊠ MY-SUITE ⊠1 ⋅1
..
==> #<TRIAL (MY-SUITE) UNEXPECTED-FAILURE 0.000s ⊠1 ⋅1>
```

Note that `SHOULD-WORK` is still run, and its check's success is
counted as evidenced by`⋅1`. The above effect can also be achieved
without running the tests again with REPLAY-EVENTS.

##### Debugging

Let's figure out what went wrong:

```
(my-suite)

;;; Here the debugger is invoked:
UNEXPECTED-FAILURE in check:
  (IS (= #1=(FOO) 5))
where
  #1# = 4
Restarts:
 0: [RECORD-EVENT] Record the event and continue.
 1: [FORCE-EXPECTED-SUCCESS] Change outcome to TRY:EXPECTED-RESULT-SUCCESS.
 2: [FORCE-UNEXPECTED-SUCCESS] Change outcome to TRY:UNEXPECTED-RESULT-SUCCESS.
 3: [FORCE-EXPECTED-FAILURE] Change outcome to TRY:EXPECTED-RESULT-FAILURE.
 4: [ABORT-CHECK] Change outcome to TRY:RESULT-ABORT*.
 5: [SKIP-CHECK] Change outcome to TRY:RESULT-SKIP.
 6: [RETRY-CHECK] Retry check.
 7: [ABORT-TRIAL] Record the event and abort trial TRY::MY-SUITE.
 8: [SKIP-TRIAL] Record the event and skip trial TRY::MY-SUITE.
 9: [RETRY-TRIAL] Record the event and retry trial TRY::MY-SUITE.
 10: [SET-TRY-DEBUG] Supply a new value for :DEBUG of TRY:TRY.
 11: [RETRY] Retry SLIME interactive evaluation request.
```

In the [SLIME](https://common-lisp.net/project/slime/doc/html/)
debugger, we press `v` on the frame of the call to `MY-SUITE` to
navigate to its definition, realize what the problem is and fix
`FOO`:

```common-lisp
(defun foo ()
  5)
```

Now, we select the `RETRY-TRIAL` restart, and on the retry
`MY-SUITE` passes. The full output is:

```
MY-SUITE
  SHOULD-WORK
    ⋅ (IS T)
  ⋅ SHOULD-WORK ⋅1
WARNING: redefining TRY::FOO in DEFUN
  ⊠ (IS (= #1=(FOO) 5))
    where
      #1# = 4
MY-SUITE retry #1
  SHOULD-WORK
    ⋅ (IS T)
  ⋅ SHOULD-WORK ⋅1
  ⋅ (IS (= (FOO) 5))
⋅ MY-SUITE ⋅2
```

##### Rerunning Stuff

Instead of working interactively, one can fix the failing test and
rerun it. Now, let's fix `MY-SUITE` and rerun it:

```common-lisp
(deftest my-suite ()
  (should-work)
  (is nil))

(try 'my-suite)
.. MY-SUITE
..   SHOULD-WORK
..     ⋅ (IS T)
..   ⋅ SHOULD-WORK ⋅1
..   ⊠ (IS NIL)
.. ⊠ MY-SUITE ⊠1 ⋅1
..
==> #<TRIAL (MY-SUITE) UNEXPECTED-FAILURE 0.000s ⊠1 ⋅1>

(deftest my-suite ()
  (should-work)
  (is t))

(try !)
.. MY-SUITE
..   ⋅ (IS T)
.. ⋅ MY-SUITE ⋅1
..
==> #<TRIAL (MY-SUITE) EXPECTED-SUCCESS 0.004s ⋅1>
```

Here, `!` refers to the most recent TRIAL returned by TRY. When a
trial is passed to TRY or is `FUNCALL`ed, trials in it that match
the type in TRY's RERUN argument are rerun (here, UNEXPECTED by
default). `SHOULD-WORK` and its check are `EXPECTED-SUCCESS`es,
hence they don't match UNEXPECTED and are not rerun.

##### Conditional Execution

Conditional execution can be achieved simply testing the TRIAL
object returned by @TRY/TESTS.

```
(deftest my-suite ()
  (when (passedp (should-work))
    (is t :msg "a test that depends on SHOULD-WORK")
    (when (is nil)
      (is nil :msg "never run"))))
```

##### Skipping

Sometimes, we do not know up front that a test should not be
executed. Calling SKIP-TRIAL unwinds from the CURRENT-TRIAL and sets
it skipped.

```common-lisp
(deftest my-suite ()
  (is t)
  (skip-trial)
  (is nil))

(my-suite)
==> #<TRIAL (MY-SUITE) SKIP 0.000s ⋅1>
```

In the above, `(IS T)` was executed, but `(IS NIL)` was not.

##### Expecting Outcomes

```common-lisp
(deftest known-broken ()
  (with-failure-expected (t)
    (is nil)))

(known-broken)
.. KNOWN-BROKEN
..   × (IS NIL)
.. ⋅ KNOWN-BROKEN ×1
..
==> #<TRIAL (KNOWN-BROKEN) EXPECTED-SUCCESS 0.000s ×1>
```

`×` marks EXPECTED-FAILUREs. `(WITH-SKIP (T) ...)` makes all checks
successes and failures EXPECTED, which are counted in their own
*CATEGORIES* by default but don't make the enclosing tests to fail.
Also see WITH-EXPECTED-OUTCOME.

##### Running Tests on Definition

With *RUN-DEFTEST-WHEN*, tests on in various EVAL-WHEN situations.
To run tests on evaluation, as in SLIME `C-M-x`, `slime-eval-defun`:

```common-lisp
(setq *run-deftest-when* :execute)

(deftest some-test ()
  (is t))
.. SOME-TEST
..   ⋅ (IS T)
.. ⋅ SOME-TEST ⋅1
..
=> SOME-TEST

(setq *run-deftest-when* nil)
```

##### Fixtures

There is no direct support for fixtures in Try. One can easily write
macros like the following.

```
(defvar *server* nil)

(defmacro with-xxx (&body body)
  `(flet ((,with-xxx-body ()
            ,@body))
     (if *server*
         (with-xxx-body)
         (with-server (make-expensive-server)
           (with-xxx-body)))))
```

Plus, with support for selectively @TRY/RERUN, the need for fixtures
is lessened.

##### Packages

The suggested way of writing tests is to call test functions
explicitly:

```
(defpackage :some-test-package
  (:use #:common-lisp #:try))
(in-package :some-test-package)

(deftest test-all ()
  (test-this)
  (test-that))

(deftest test-this ()
  (test-this/more))

(deftest test-this/more ()
  (is t))

(deftest test-that ()
  (is t))

(deftest not-called ()
  (is t))

(defun test ()
  (warn-on-tests-not-run ((find-package :some-test-package))
    (try 'test-all)))

(test)
.. TEST-ALL
..   TEST-THIS
..     TEST-THIS/MORE
..       ⋅ (IS T)
..     ⋅ TEST-THIS/MORE ⋅1
..   ⋅ TEST-THIS ⋅1
..   TEST-THAT
..     ⋅ (IS T)
..   ⋅ TEST-THAT ⋅1
.. ⋅ TEST-ALL ⋅2
.. WARNING: Test NOT-CALLED not run.
==> #<TRIAL (TEST-ALL) EXPECTED-SUCCESS 0.012s ⋅2>
```

Note how the TEST function uses WARN-ON-TESTS-NOT-RUN to catch any
tests defined in `SOME-TEST-PACKAGE` that were not run. Tests can be
deleted by FMAKUNBOUND, UNINTERN, or by redefining the function with
DEFUN. Tests defined in a given package can be listed with
LIST-PACKAGE-TESTS.

This style allows higher level tests to establish the dynamic
environment necessary for lower level tests.

## Emacs Integration

The Elisp `mgl-try` interactive command runs a Try test and
displays its output in a `lisp-mode` buffer with minor modes
`outline-mode` and `mgl-try-mode`. It is assumed that the lisp is
running under [Slime](https://slime.common-lisp.dev/). In the
buffer,

- use `M-.` to visit a test function;

- move between UNEXPECTED events with keys `p` and `n`;

- move between events which are not EXPECTED-SUCCESSes with `P`
  and `N`;

- rerun the most recent trial (TRY:!) with `r` (subject to the
  filtering described @TRY/RERUN);

- rerun the most recently finished test with `R` (and all tests it
  calls);

- run an arbitrary test with `t` (defaults to symbol under point);

- some low-level outline mode commands are also given convenient
  bindings:

        <tab>           outline-cycle
        C-p             outline-previous-visible-heading
        C-n             outline-next-visible-heading
        U               outline-up-heading


### Emacs Setup

Load `src/mgl-try.el` in Emacs.

If you installed Try with Quicklisp, the location of `mgl-try.el`
may change with updates, and you may want to copy the current
version of `mgl-try.el` to a stable location:

    (try:install-try-elisp "~/quicklisp/")

Then, assuming the Elisp file is in the quicklisp directory, add
something like this to your `.emacs`:

```elisp
(load "~/quicklisp/mgl-try.el")
```


- [function] INSTALL-TRY-ELISP TARGET-DIR

    Copy `mgl-try.el` distributed with this package to TARGET-DIR.

## Events

Try is built around events implemented as CONDITIONs.
Matching the types of events to *DEBUG*, *COUNT*, *COLLECT*, *RERUN*,
*PRINT*, and *DESCRIBE* is what gives Try its flexibility.

### Middle Layer of Events

The event hierarchy is fairly involved, so let's start in the middle.
The condition EVENT has 4 disjoint subclasses:

- TRIAL-START, which corresponds to the entry to a test (see
  @TRY/TESTS),

- VERDICT, the OUTCOME of a TRIAL,

- RESULT, the OUTCOME of a check (see @TRY/CHECKS), and

- ERROR\*, an unexpected CL:ERROR or unadorned non-local exit.

```common-lisp
(let (;; We don't want to debug nor print a backtrace for the error below.
      (*debug* nil)
      (*describe* nil))
  ;; signals TRIAL-START / VERDICT-ABORT* on entry / exit
  (with-test (demo)
    ;; signals EXPECTED-RESULT-SUCCESS
    (is t)
    ;; signals UNHANDLED-ERROR with a nested CL:ERROR
    (error "xxx")))
.. DEMO                       ; TRIAL-START
..   ⋅ (IS T)                 ; EXPECTED-RESULT-SUCCESS (⋅)
..   ⊟ "xxx" (SIMPLE-ERROR)   ; UNHANDLED-ERROR (⊟)
.. ⊟ DEMO ⊟1 ⋅1               ; VERDICT-ABORT* (⊟)
..
==> #<TRIAL (WITH-TEST (DEMO)) ABORT* 0.004s ⊟1 ⋅1>
```


### Concrete Events

The non-abstract condition classes of events that are actually
signalled are called concrete.

TRIAL-START is a concrete event class. RESULTs and VERDICTs have six
 concrete subclasses:

- EXPECTED-RESULT-SUCCESS, UNEXPECTED-RESULT-SUCCESS,
   EXPECTED-RESULT-FAILURE, UNEXPECTED-RESULT-FAILURE,
   RESULT-SKIP, RESULT-ABORT\*

- EXPECTED-VERDICT-SUCCESS, UNEXPECTED-VERDICT-SUCCESS,
   EXPECTED-VERDICT-FAILURE, UNEXPECTED-VERDICT-FAILURE,
   VERDICT-SKIP, VERDICT-ABORT\*

ERROR\* is an abstract class with two concrete subclasses:

- UNHANDLED-ERROR, signalled when a CL:ERROR reaches the handler set
   up by DEFTEST or WITH-TEST, or when the debugger is invoked.

- NLX, signalled when no error was detected by the handler, but the
   trial finishes with a non-local exit.

These are the 15 concrete event classes.

### Event Glue

These condition classes group various bits of the
@TRY/CONCRETE-EVENTS and the @TRY/MIDDLE-LAYER-OF-EVENTS for ease of
reference.

Concrete event classes except TRIAL-START are subclasses of
hyphen-separated words in their name. For example,
UNEXPECTED-RESULT-FAILURE inherits from UNEXPECTED, RESULT, and
FAILURE, so it matches types such as UNEXPECTED or `(AND UNEXPECTED
RESULT)`.

- [condition] EVENT

    Common abstract superclass of all events in Try.

- [condition] EXPECTED EVENT

    Concrete condition classes with EXPECTED in their
    name are subclasses of EXPECTED. SKIP is also a subclass of
    EXPECTED.

- [condition] UNEXPECTED EVENT

    Concrete condition classes with UNEXPECTED in their
    name are subclasses of UNEXPECTED. ABORT\* is also a subclass of
    UNEXPECTED.

- [condition] SUCCESS EVENT

    See @TRY/CHECKS and @TRY/TRIAL-VERDICTS for how
    SUCCESS or FAILURE is decided.

- [condition] FAILURE EVENT

    See SUCCESS.

- [condition] DISMISSAL EVENT

    The third possibility after SUCCESS and FAILURE.
    Either SKIP or ABORT\*.

- [condition] ABORT* UNEXPECTED

    `RESULT-ABORT*`, `VERDICT-ABORT*` or ERROR\*.

- [condition] SKIP EXPECTED DISMISSAL

    RESULT-SKIP or VERDICT-SKIP.

- [condition] LEAF EVENT

    RESULT or ERROR\*.

- [type] EXPECTED-SUCCESS

    A shorthand for `(AND EXPECTED SUCCESS)`.

- [type] UNEXPECTED-SUCCESS

    A shorthand for `(AND UNEXPECTED SUCCESS)`.

- [type] EXPECTED-FAILURE

    A shorthand for `(AND EXPECTED FAILURE)`.

- [type] UNEXPECTED-FAILURE

    A shorthand for `(AND UNEXPECTED FAILURE)`.

- [type] PASS

    An OUTCOME that's not an ABORT\* or an UNEXPECTED FAILURE.

- [type] FAIL

    An ABORT\* or an UNEXPECTED FAILURE.

### Printing Events

- [variable] *EVENT-PRINT-BINDINGS* ((\*PRINT-CIRCLE\* T))

    EVENTs are conditions signalled in code that may change printer
    variables such as *PRINT-CIRCLE*, *PRINT-LENGTH*, etc. To control
    how events are printed, the list of variable bindings in
    *EVENT-PRINT-BINDINGS* is established whenever an EVENT is printed
    as if with:
    
    ```
    (progv (mapcar #'first *event-print-bindings*)
           (mapcar #'second *event-print-bindings*)
      ...)
    ```
    
    The default value ensures that shared structure is recognized (see
    @TRY/CAPTURES). If the `#N#` syntax feels cumbersome, then change
    this variable.

### Event Restarts

Only RECORD-EVENT is applicable to all EVENTs. See
@TRY/CHECK-RESTARTS, @TRY/TRIAL-RESTARTS for more.

- [function] RECORD-EVENT &OPTIONAL CONDITION

    This restart is always the first restart available when an EVENT is
    signalled running under TRY (i.e. there is a CURRENT-TRIAL). TRY
    always invokes RECORD-EVENT when handling events.

### Outcomes

- [condition] OUTCOME EVENT

    An OUTCOME is the resolution of either a TRIAL or a
    check (see @TRY/CHECKS), corresponding to subclasses VERDICT and
    RESULT.

- [macro] WITH-EXPECTED-OUTCOME (EXPECTED-TYPE) &BODY BODY

    When an OUTCOME is to be signalled, EXPECTED-TYPE determines
    whether it's going to be EXPECTED. The concrete OUTCOME classes are
    `{EXPECTED,UNEXPECTED}-{RESULT,VERDICT}-{SUCCESS,FAILURE}` (see
    @TRY/EVENTS), of which RESULT or VERDICT and SUCCESS or FAILURE are
    already known. If a RESULT FAILURE is to be signalled, then the
    moral equivalent of `(SUBTYPEP '(AND RESULT FAILURE) EXPECTED-TYPE)`
    is evaluated and depending on whether it's true,
    EXPECTED-RESULT-FAILURE or UNEXPECTED-RESULT-FAILURE is signalled.
    
    By default, SUCCESS is expected. The following example shows how to
    expect both SUCCESS and FAILURE for RESULTs, while requiring
    VERDICTs to succeed:
    
    ```common-lisp
    (let ((*debug* nil))
      (with-expected-outcome ('(or result (and verdict success)))
        (with-test (t1)
          (is nil))))
    .. T1
    ..   × (IS NIL)
    .. ⋅ T1 ×1
    ..
    ==> #<TRIAL (WITH-TEST (T1)) EXPECTED-SUCCESS 0.000s ×1>
    ```
    
    This is equivalent to `(WITH-FAILURE-EXPECTED () ...)`. To make
    result failures expected but result successes unexpected:
    
    ```common-lisp
    (let ((*debug* nil))
      (with-expected-outcome ('(or (and result failure) (and verdict success)))
        (with-test (t1)
          (is t)
          (is nil))))
    .. T1
    ..   ⊡ (IS T)
    ..   × (IS NIL)
    .. ⋅ T1 ⊡1 ×1
    ..
    ==> #<TRIAL (WITH-TEST (T1)) EXPECTED-SUCCESS 0.000s ⊡1 ×1>
    ```
    
    This is equivalent to `(WITH-FAILURE-EXPECTED ('FAILURE) ...)`. The
    final example leaves result failures unexpected but makes both
    verdict successes and failures expected:
    
    ```common-lisp
    (let ((*debug* nil))
      (with-expected-outcome ('(or (and result success) verdict))
        (with-test (t1)
          (is nil))))
    .. T1
    ..   ⊠ (IS NIL)
    .. × T1 ⊠1
    ..
    ==> #<TRIAL (WITH-TEST (T1)) EXPECTED-FAILURE 0.004s ⊠1>
    ```


- [macro] WITH-FAILURE-EXPECTED (&OPTIONAL (RESULT-EXPECTED-TYPE T) (VERDICT-EXPECTED-TYPE ''SUCCESS)) &BODY BODY

    A convenience macro on top of WITH-EXPECTED-OUTCOME,
    WITH-FAILURE-EXPECTED expects VERDICTs to have VERDICT-EXPECTED-TYPE
    and RESULTs to have RESULT-EXPECTED-TYPE. A simple
    `(WITH-FAILURE-EXPECTED () ...)` makes all RESULT SUCCESSes and
    FAILUREs EXPECTED. `(WITH-FAILURE-EXPECTED ('FAILURE) ..)` expects
    FAILUREs only, and any SUCCESSes will be UNEXPECTED.

- [macro] WITH-SKIP (&OPTIONAL (SKIP T)) &BODY BODY

    WITH-SKIP skips checks and trials. It forces an immediate
    SKIP-TRIAL whenever a trial is started (which turns into a
    VERDICT-SKIP) and makes checks (without intervening trials, of
    course) evaluate normally but signal RESULT-SKIP. SKIP is NIL
    cancels the effect of any enclosing WITH-SKIP with SKIP true.

#### Outcome Restarts

- [function] FORCE-EXPECTED-SUCCESS &OPTIONAL CONDITION

    Change the type of the OUTCOME being signalled to EXPECTED and
    SUCCESS. If the original condition is a RESULT, then this will be
    EXPECTED-RESULT-SUCCESS, if it is a VERDICT, then
    EXPECTED-VERDICT-SUCCESS.

- [function] FORCE-UNEXPECTED-SUCCESS &OPTIONAL CONDITION

    Change the type of OUTCOME being signalled to UNEXPECTED and
    SUCCESS.

- [function] FORCE-EXPECTED-FAILURE &OPTIONAL CONDITION

    Change the type of OUTCOME being signalled to EXPECTED and
    FAILURE.

- [function] FORCE-UNEXPECTED-FAILURE &OPTIONAL CONDITION

    Change the type of OUTCOME being signalled to UNEXPECTED and
    FAILURE.

#### Checks

Checks are like CL:ASSERTs, they check whether some condition holds
and signal an OUTCOME. The outcome signalled for checks is a
subclass of RESULT.

Take, for example, `(IS (= X 5))`. Depending on whether `X` is
indeed 5, some kind of RESULT SUCCESS or FAILURE will be signalled.
WITH-EXPECTED-OUTCOME determines whether it's EXPECTED or
UNEXPECTED, and we have one of EXPECTED-RESULT-SUCCESS,
UNEXPECTED-RESULT-SUCCESS, EXPECTED-RESULT-FAILURE,
UNEXPECTED-RESULT-FAILURE to signal. Furthermore, if WITH-SKIP is in
effect, then RESULT-SKIP is signalled.

The result is signalled with `#'SIGNAL` if it is a PASS, else it's
signalled with `#'ERROR`. This distinction matters only if the event
is not handled, which is never the case in a TRIAL. Standalone
checks though - those that are not enclosed by a trial - invoke the
debugger on RESULTs which are not of type PASS.

The signalled RESULT is not final until RECORD-EVENT is invoked on
it, and it can be changed with the @TRY/OUTCOME-RESTARTS and the
@TRY/CHECK-RESTARTS.

- [condition] RESULT LEAF OUTCOME

- [condition] EXPECTED-RESULT-SUCCESS EXPECTED RESULT SUCCESS

- [condition] UNEXPECTED-RESULT-SUCCESS UNEXPECTED RESULT SUCCESS

- [condition] EXPECTED-RESULT-FAILURE EXPECTED RESULT FAILURE

- [condition] UNEXPECTED-RESULT-FAILURE UNEXPECTED RESULT FAILURE

- [condition] RESULT-SKIP RESULT SKIP

- [condition] RESULT-ABORT* RESULT ABORT\* DISMISSAL

##### Check Restarts

- [function] ABORT-CHECK &OPTIONAL CONDITION

    Change the OUTCOME of the check being signalled to `RESULT-ABORT*`.
    `RESULT-ABORT*`, being `(NOT PASS)`, will cause the check to return
    NIL if RECORD-EVENT is invoked on it.

- [function] SKIP-CHECK &OPTIONAL CONDITION

    Change the OUTCOME of the check being signalled to RESULT-SKIP.
    RESULT-SKIP, being a PASS, will cause the check to return T if
    CONTINUE or RECORD-EVENT is invoked on it.

- [function] RETRY-CHECK &OPTIONAL CONDITION

    Initiate a non-local exit to go reevaluate the forms
    wrapped by the check without signalling an OUTCOME.

#### Trials

- [class] TRIAL FUNCALLABLE-STANDARD-OBJECT

    Trials are records of calls to tests (see
    @TRY/COUNT, @TRY/COLLECT). Their behaviour as @FUNCALLABLE-INSTANCEs
    is explained in @TRY/RERUN.
    
    There are three ways to acquire a TRIAL object: by calling
    CURRENT-TRIAL, through the lexical binding of the symbol that names
    the test or through the return value of a test:
    
    ```common-lisp
    (deftest xxx ()
      (prin1 xxx))
    
    (xxx)
    .. #<TRIAL (XXX) RUNNING>
    ==> #<TRIAL (XXX) EXPECTED-SUCCESS 0.000s>
    ```
    
    WITH-TRIAL can also provide access to its TRIAL:
    
    ```common-lisp
    (with-test (t0)
      (prin1 t0))
    .. #<TRIAL (WITH-TEST (T0)) RUNNING>
    ==> #<TRIAL (WITH-TEST (T0)) EXPECTED-SUCCESS 0.000s>
    ```
    
    TRIALs are not to be instantiated by client code.

- [function] CURRENT-TRIAL

    TRIALs, like the calls to tests they stand for, nest. CURRENT-TRIAL
    returns the innermost trial. If there is no currently running test,
    then an error is signalled. The returned trial is RUNNINGP.

##### Trial Events

- [condition] TRIAL-EVENT EVENT

    A TRIAL-EVENT is either a TRIAL-START or a
    VERDICT.

- [reader] TRIAL TRIAL-EVENT (:TRIAL)

- [condition] TRIAL-START TRIAL-EVENT

    TRIAL-START is signalled when a test function
    (see @TRY/TESTS) is entered and a TRIAL is started, it is already
    the CURRENT-TRIAL, and the @TRY/TRIAL-RESTARTS are available. It is
    also signalled when a trial is retried:
    
    ```common-lisp
    (let ((*print* nil)
          (n 0))
      (with-test ()
        (handler-bind ((trial-start (lambda (c)
                                      (format t "TRIAL-START for ~S retry#~S~%"
                                              (test-name (trial c))
                                              (n-retries (trial c))))))
          (with-test (this)
            (incf n)
            (when (< n 3)
              (retry-trial))))))
    .. TRIAL-START for THIS retry#0
    .. TRIAL-START for THIS retry#1
    .. TRIAL-START for THIS retry#2
    ..
    ```
    
    The matching of TRIAL-START events is less straightforward than that
    of other EVENTs.
    
    - When a TRIAL-START event matches the `COLLECT` type (see
      @TRY/COLLECT), its TRIAL is collected.
    
    - Similarly, when a TRIAL-START matches the PRINT
      type (see @TRY/PRINT), it is printed immediately, and its trial's
      VERDICT will be printed too regardless of whether it matches
      PRINT. If TRIAL-START does not match
      PRINT, it may still be printed if for example
      *PRINT-PARENT* requires it.
    
    - When a TRIAL-START matches the `RERUN` type (see @TRY/RERUN), its
      TRIAL may be rerun.
    
    - Also, see WITH-SKIP.


- [condition] VERDICT TRIAL-EVENT OUTCOME

    A VERDICT is the OUTCOME of a TRIAL. It is one of
    `{EXPECTED,UNEXPECTED}-VERDICT-{SUCCESS,FAILURE}`, VERDICT-SKIP and
    VERDICT-ABORT\*. Regarding how the verdict type is determined, see
    @TRY/TRIAL-VERDICTS.
    
    Verdicts are signalled while their TRIAL is
    still the CURRENT-TRIAL, and @TRY/TRIAL-RESTARTS are still
    available.
    
    ```common-lisp
    (try (lambda ()
           (handler-bind (((and verdict failure) #'retry-trial))
             (with-test (this)
               (is (zerop (random 2)))))))
    .. (TRY #<FUNCTION (LAMBDA ()) {53038ADB}>)
    ..   THIS
    ..     ⊠ (IS (ZEROP #1=(RANDOM 2)))
    ..       where
    ..         #1# = 1
    ..   THIS retry #1
    ..     ⋅ (IS (ZEROP (RANDOM 2)))
    ..   ⋅ THIS ⋅1
    .. ⋅ (TRY #<FUNCTION (LAMBDA ()) {53038ADB}>) ⋅1
    ..
    ==> #<TRIAL (TRY #<FUNCTION (LAMBDA ()) {53038ADB}>) EXPECTED-SUCCESS 0.000s ⋅1>
    ```


- [condition] EXPECTED-VERDICT-SUCCESS EXPECTED VERDICT SUCCESS

- [condition] UNEXPECTED-VERDICT-SUCCESS UNEXPECTED VERDICT SUCCESS

- [condition] EXPECTED-VERDICT-FAILURE EXPECTED VERDICT FAILURE

- [condition] UNEXPECTED-VERDICT-FAILURE UNEXPECTED VERDICT FAILURE

- [condition] VERDICT-SKIP VERDICT SKIP

- [condition] VERDICT-ABORT* VERDICT ABORT\* DISMISSAL

##### Trial Verdicts

When a trial finished, a VERDICT is signalled. The verdict's type
is determined as follows.

- It is a VERDICT-SKIP if

    - SKIP-TRIAL was called on the trial, or

    - ABORT-TRIAL, SKIP-TRIAL, or RETRY-TRIAL was called on an
      enclosing trial, and

    - these were not overruled by a later ABORT-TRIAL or RETRY-TRIAL
      on the trial.

- It is a VERDICT-ABORT\* if ABORT-TRIAL was called on the trial, and
  it wasn't overruled by a later SKIP-TRIAL or RETRY-TRIAL.

- If all children (including those not collected in CHILDREN) of the
  trial PASS, then the verdict will be a SUCCESS, else it will be a
  FAILURE.

- Subject to the WITH-EXPECTED-OUTCOME in effect,
  `{EXPECTED,UNEXPECTED}-VERDICT-{SUCCESS,FAILURE}` is the type of
  the verdict which will be signalled.

The verdict of this type is signalled, but its type can be changed
by the @TRY/OUTCOME-RESTARTS or the @TRY/TRIAL-RESTARTS before
RECORD-EVENT is invoked on it.

- [reader] VERDICT TRIAL (= NIL)

    The VERDICT EVENT signalled when this
    TRIAL finished or NIL if it has not finished yet.

- [function] RUNNINGP TRIAL

    See if the function call associated with TRIAL has not returned yet.
    Trials that are not running have a VERDICT and are said to be
    finished.

- [function] PASSEDP TRIAL

    See if TRIAL has finished and its VERDICT is a
    PASS.

- [function] FAILEDP TRIAL

    See if TRIAL has finished and its VERDICT is a
    FAIL.

##### Trial Restarts

There are three restarts available for manipulating running
trials: ABORT-TRIAL, SKIP-TRIAL, and RETRY-TRIAL. They may be
invoked programatically or from the debugger. ABORT-TRIAL is also
invoked by TRY when encountering UNHANDLED-ERROR.

The functions below invoke one of these restarts associated with a
TRIAL. It is an error to call them on trials that are not RUNNINGP,
but they may be called on trials other than the CURRENT-TRIAL. In
that case, any intervening trials are skipped.

```common-lisp
;; Skipped trials are marked with '-' in the output.
(with-test (outer)
  (with-test (inner)
    (is t)
    (skip-trial nil outer)))
.. OUTER
..   INNER
..     ⋅ (IS T)
..   - INNER ⋅1
.. - OUTER ⋅1
..
==> #<TRIAL (WITH-TEST (OUTER)) SKIP 0.000s ⋅1>
```

Furthermore, all three restarts initiate a non-local exit to
return from the trial. If during the unwinding of the stack, the
non-local-exit is cancelled (see @CANCELLED-NLX), the appropriate
restart will be invoked upon returning from the trial. In the
following example, the non-local exit from a skip is cancelled by a
THROW.

```common-lisp
(with-test (some-test)
  (catch 'foo
    (unwind-protect
         (skip-trial)
      (throw 'foo nil)))
  (is t :msg "check after skip"))
.. SOME-TEST
..   ⋅ check after skip
.. - SOME-TEST ⋅1
..
==> #<TRIAL (WITH-TEST (SOME-TEST)) SKIP 0.000s ⋅1>
```

In the next example, the non-local exit from a skip is cancelled by
an ERROR, which triggers an ABORT-TRIAL.

```common-lisp
(let ((*debug* nil)
      (*describe* nil))
  (with-test (foo)
    (unwind-protect
         (skip-trial)
      (error "xxx"))))
.. FOO
..   ⊟ "xxx" (SIMPLE-ERROR)
.. ⊟ FOO ⊟1
..
==> #<TRIAL (WITH-TEST (FOO)) ABORT* 0.000s ⊟1>
```

All three restarts may be invoked on any EVENT, including the
trial's own TRIAL-START and VERDICT. If their CONDITION
argument is an EVENT (RETRY-TRIAL has a special case here), they
also record it (as in RECORD-EVENT) to ensure that when they handle
an EVENT in the debugger or programatically that event is not
dropped.

- [function] ABORT-TRIAL &OPTIONAL CONDITION (TRIAL (CURRENT-TRIAL))

    Invoke the ABORT-TRIAL restart of a RUNNINGP TRIAL.
    
    When CONDITION is a VERDICT for TRIAL, ABORT-TRIAL signals a new
    verdict of type VERDICT-ABORT\*. This behavior is similar to that
    of ABORT-CHECK. Else, the ABORT-TRIAL restart may record CONDITION,
    then it initiates a non-local exit to return from the test
    function with VERDICT-ABORT\*. If during the unwinding SKIP-TRIAL
    or RETRY-TRIAL is called, then the abort is cancelled.
    
    Since ABORT\* is an UNEXPECTED EVENT, ABORT-TRIAL is rarely used
    programatically. Signalling any error in a trial that's not caught
    before the trial's handler catches it will get turned into an
    UNHANDLED-ERROR, and TRY will invoke ABORT-TRIAL with it. Thus,
    instead of invoking ABORT-TRIAL directly, signalling an error will
    often suffice.

- [function] SKIP-TRIAL &OPTIONAL CONDITION (TRIAL (CURRENT-TRIAL))

    Invoke the SKIP-TRIAL restart of a RUNNINGP TRIAL.
    
    When CONDITION is a VERDICT for TRIAL, SKIP-TRIAL signals a new
    verdict of type VERDICT-SKIP. This behavior is similar to that of
    SKIP-CHECK. Else, the SKIP-TRIAL restart may record CONDITION, then
    it initiates a non-local exit to return from the test function with
    VERDICT-SKIP. If during the unwinding ABORT-TRIAL or RETRY-TRIAL is
    called, then the skip is cancelled.
    
    ```common-lisp
    (with-test (skipped)
      (handler-bind ((unexpected-result-failure #'skip-trial))
        (is nil)))
    .. SKIPPED
    ..   ⊠ (IS NIL)
    .. - SKIPPED ⊠1
    ..
    ==> #<TRIAL (WITH-TEST (SKIPPED)) SKIP 0.000s ⊠1>
    ```
    
    Invoking SKIP-TRIAL on the TRIAL's own TRIAL-START skips the trial
    being started.
    
    ```common-lisp
    (let ((*print* '(or outcome leaf)))
      (with-test (parent)
        (handler-bind ((trial-start #'skip-trial))
          (with-test (child)
            (is nil)))))
    .. PARENT
    ..   - CHILD
    .. ⋅ PARENT
    ..
    ```


- [function] RETRY-TRIAL &OPTIONAL CONDITION (TRIAL (CURRENT-TRIAL))

    Invoke the RETRY-TRIAL restart of RUNNINGP TRIAL. The RETRY-TRIAL
    restart may record CONDITION, then it initiates a non-local
    exit to go back to the beginning of the test function. If the
    non-local exit completes, then
    
    - (N-RETRIES TRIAL) is incremented,
    
    - collected results and trials are cleared (see @TRY/COLLECT),
    
    - counts are zeroed (see @TRY/COUNT), and
    
    - TRIAL-START is signalled again.
    
    If during the unwinding ABORT-TRIAL or SKIP-TRIAL is called, then
    the retry is cancelled.
    
    CONDITION (which may be NIL) is recorded if it is an EVENT but not
    the VERDICT of TRIAL, and the RECORD-EVENT restart is available.

- [reader] N-RETRIES TRIAL (:N-RETRIES = 0)

    The number of times this TRIAL has
    been retried. See RETRY-TRIAL.

### Errors

- [condition] ERROR* ABORT\* TRIAL-EVENT LEAF

    Either UNHANDLED-ERROR or NLX, ERROR\* causes or
    represents abnormal termination of a TRIAL. ABORT-TRIAL can be
    called with ERROR\*s, but there is little need for explicitly doing
    so as RECORD-EVENT, which TRY invokes, takes care of this.

- [reader] TEST-NAME ERROR\* (:TEST-NAME)

- [condition] UNHANDLED-ERROR ERROR\*

    Signalled when an CL:ERROR condition reaches the
    handlers set up DEFTEST or WITH-TEST, or when their *DEBUGGER-HOOK*
    is invoked with a condition that's not an EVENT.

- [reader] NESTED-CONDITION UNHANDLED-ERROR (:CONDITION = 'NIL)

- [reader] BACKTRACE-OF UNHANDLED-ERROR (:BACKTRACE = 'NIL)

- [reader] DEBUGGER-INVOKED-P UNHANDLED-ERROR (:DEBUGGER-INVOKED-P = 'NIL)

- [variable] *GATHER-BACKTRACE* T

    Capturing the backtrace can be expensive. *GATHER-BACKTRACE*
    controls whether UNHANDLED-ERRORs shall have their BACKTRACE-OF
    populated.

- [condition] NLX ERROR\*

    Representing a non-local exit of unknown
    origin, this is signalled if a TRIAL does not return normally
    although it should have because it was not dismissed (see DISMISSAL,
    SKIP-TRIAL, ABORT-TRIAL). In this case, there is no CL:ERROR
    associated with the event.

### Categories

Categories determine how event types are printed and events of
what types are counted together.

The default value of *CATEGORIES* is

```
((abort*             :marker "⊟")
 (unexpected-failure :marker "⊠")
 (unexpected-success :marker "⊡")
 (skip               :marker "-")
 (expected-failure   :marker "×")
 (expected-success   :marker "⋅"))
```

which says that all concrete EVENTs that are of type ABORT\* (i.e.
`RESULT-ABORT*`, `VERDICT-ABORT*`, UNHANDLED-ERROR, and NLX) are to
be marked with `"⊟"` when printed (see @TRY/PRINT). Also, the six
types define six counters for @TRY/COUNT. Note that UNEXPECTED
events have the same marker but squared as their EXPECTED
counterpart.

- [variable] *CATEGORIES* "- see above -"

    A list of of elements like `(TYPE &KEY MARKER)`.
    When @TRY/PRINT, @TRY/CONCRETE-EVENTS are printed with the marker of
    the first matching type. When @TRY/COUNT, the counts associated with
    all matching types are incremented.

- [function] FANCY-STD-CATEGORIES

    Returns the default value of *CATEGORIES* (see @TRY/CATEGORIES),
    which contains some fancy Unicode characters.

- [function] ASCII-STD-CATEGORIES

    Returns a value suitable for *CATEGORIES*, which uses only ASCII
    characters for the markers.
    
    ```
    '((abort*             :marker "!")
      (unexpected-failure :marker "F")
      (unexpected-success :marker ":")
      (skip               :marker "-")
      (expected-failure   :marker "f")
      (expected-success   :marker "."))
    ```


## The IS Macro

IS is the fundamental one among @TRY/CHECKS, on which all
the others are built, and it is a replacement for CL:ASSERT that can
capture values of subforms to provide context to failures:

```common-lisp
(is (= (1+ 5) 0))
.. debugger invoked on UNEXPECTED-RESULT-FAILURE:
..   UNEXPECTED-FAILURE in check:
..     (IS (= #1=(1+ 5) 0))
..   where
..     #1# = 6
```

IS automatically captures values of arguments to functions like `1+`
in the above example. Values of other interesting subforms can be
explicitly requested to be captured. IS supports capturing multiple
values and can be taught how to deal with macros. The combination of
these features allows MATCH-VALUES to be implementable as tiny
extension:

```common-lisp
(is (match-values (values (1+ 5) "sdf")
      (= * 0)
      (string= * "sdf")))
.. debugger invoked on UNEXPECTED-RESULT-FAILURE:
..   UNEXPECTED-FAILURE in check:
..     (IS
..      (MATCH-VALUES #1=(VALUES (1+ 5) #2="sdf")
..        (= * 0)
..        (STRING= * "sdf")))
..   where
..     #1# == 6
..            #2#
```

IS is flexible enough that all other checks (SIGNALS, SIGNALS-NOT,
INVOKES-DEBUGGER, INVOKES-DEBUGGER-NOT, FAILS, and IN-TIME are built
on top of it.

- [macro] IS FORM &KEY MSG CTX (CAPTURE T) (PRINT-CAPTURES T) (RETRY T)

    Evaluate FORM and signal a RESULT SUCCESS if its first return
    value is not NIL, else signal a RESULT FAILURE (see @TRY/OUTCOMES).
    IS returns normally if
    
    - the RECORD-EVENT restart is invoked (available when running in a
      trial), or
    
    - the CONTINUE restart is invoked (available when not running in a
      trial), or
    
    - the signalled RESULT condition is not handled (possible only when
      not running in a trial, and the result is a PASS).
    
    The return value of IS is T if the last condition signalled is a
    SUCCESS, and NIL otherwise.
    
    MSG and CTX are @TRY/FORMAT-SPECIFIER-FORMS. MSG prints a
    description of the check being made, which is by default the whole
    IS form. Due to how conditions are printed, MSG says what the
    desired outcome is, and CTX provides information about the
    evaluation.
    
    ```common-lisp
    (is (equal (prin1-to-string 'hello) "hello")
        :msg "Symbols are replacements for strings." 
        :ctx ("*PACKAGE* is ~S and *PRINT-CASE* is ~S~%"
              *package* *print-case*))
    .. debugger invoked on UNEXPECTED-RESULT-FAILURE:
    ..   UNEXPECTED-FAILURE in check:
    ..     Symbols are replacements for strings.
    ..   where
    ..     (PRIN1-TO-STRING 'HELLO) = "HELLO"
    ..   *PACKAGE* is #<PACKAGE "TRY"> and *PRINT-CASE* is :UPCASE
    ..
    ```
    
    If CAPTURE is true, the value(s) of some subforms of FORM may be
    automatically recorded in the condition and also made available for
    CTX via *IS-CAPTURES*. See @TRY/CAPTURES for more.
    
    If PRINT-CAPTURES is true, the captures made are printed when the
    RESULT condition is displayed in the debugger or `*DESCRIBE*`d (see
    @TRY/PRINT). This is the `where (PRIN1-TO-STRING 'HELLO) ="HELLO"`
    part above. If PRINT-CAPTURES is NIL, the captures are still
    available in *IS-CAPTURES* for writing custom CTX messages.
    
    If RETRY is true, then the RETRY-CHECK restart evaluates FORM again
    and signals a new RESULT. If RETRY is NIL, then the RETRY-CHECK
    restart returns :RETRY, which allows complex checks such as SIGNALS
    to implement their own retry mechanism.

- [variable] *IS-FORM*

    IS binds this to its FORM argument for CTX and MSG.

- [variable] *IS-CAPTURES*

    Captures made during an IS evaluation are made available for
    CTX via *IS-CAPTURES*.

### Format Specifier Forms

A format specifier form is a Lisp form, typically an argument to
macro, standing for the FORMAT-CONTROL and FORMAT-ARGS arguments to
the FORMAT function.

It may be a constant string:

```common-lisp
(is nil :msg "FORMAT-CONTROL~%with no args.")
.. debugger invoked on UNEXPECTED-RESULT-FAILURE:
..   UNEXPECTED-FAILURE in check:
..     FORMAT-CONTROL
..     with no args.
```

It may be a list whose first element is a constant string, and the
rest are the format arguments to be evaluated:

```common-lisp
(is nil :msg ("Implicit LIST ~A." "form"))
.. debugger invoked on UNEXPECTED-RESULT-FAILURE:
..   UNEXPECTED-FAILURE in check:
..     Implicit LIST form.
```

Or it may be a form that evaluates to a list like `(FORMAT-CONTROL
&REST FORMAT-ARGS)`:

```common-lisp
(is nil :msg (list "Full ~A." "form"))
.. debugger invoked on UNEXPECTED-RESULT-FAILURE:
..   UNEXPECTED-FAILURE in check:
..     Full form.
```

Finally, it may evaluate to NIL, in which case some context specific
default is implied.

- [function] CANONICALIZE-FORMAT-SPECIFIER-FORM FORM

    Ensure that the format specifier form FORM is in its full form.

### Captures

During the evaluation of the FORM argument of IS, evaluation of any
form (e.g. a subform of FORM) may be recorded, which are called
captures.

#### Automatic Captures

IS automatically captures some subforms of FORM that are likely
to be informative. In particular, if FORM is a function call, then
non-constant arguments are automatically captured:

```common-lisp
(is (= 3 (1+ 2) (- 4 3)))
.. debugger invoked on UNEXPECTED-RESULT-FAILURE:
..   UNEXPECTED-FAILURE in check:
..     (IS (= 3 #1=(1+ 2) #2=(- 4 3)))
..   where
..     #1# = 3
..     #2# = 1
```

By default, automatic captures are not made for subforms deeper in
FORM, except for when FORM is a call to NULL,
ENDP and NOT:

```common-lisp
(is (null (find (1+ 1) '(1 2 3))))
.. debugger invoked on UNEXPECTED-RESULT-FAILURE:
..   UNEXPECTED-FAILURE in check:
..     (IS (NULL #1=(FIND #2=(1+ 1) '(1 2 3))))
..   where
..     #2# = 2
..     #1# = 2
```

```common-lisp
(is (endp (member (1+ 1) '(1 2 3))))
.. debugger invoked on UNEXPECTED-RESULT-FAILURE:
..   UNEXPECTED-FAILURE in check:
..     (IS (ENDP #1=(MEMBER #2=(1+ 1) '(1 2 3))))
..   where
..     #2# = 2
..     #1# = (2 3)
```

Note that the argument of NOT is not captured as it is
assumed to be NIL or T. If that's not true, use NULL.

```common-lisp
(is (not (equal (1+ 5) 6)))
.. debugger invoked on UNEXPECTED-RESULT-FAILURE:
..   UNEXPECTED-FAILURE in check:
..     (IS (NOT (EQUAL #1=(1+ 5) 6)))
..   where
..     #1# = 6
```

Other automatic captures are discussed with the relevant
functionality such as MATCH-VALUES.

##### Writing Automatic Capture Rules

- [class] SUB STRUCTURE-OBJECT

    A SUB (short for substitution) says that in the original form IS is
    checking, a SUBFORM was substituted (by SUBSTITUTE-IS-FORM) with
    VAR (if VALUESP is NIL) or with (VALUES-LIST VAR) if VALUESP is
    true. Conversely, VAR is to be bound to the evaluated NEW-FORM if
    VALUESP is NIL, and to (MULTIPLE-VALUE-LIST FORM) if VALUESP.
    NEW-FORM is often `EQ` to SUBFORM, but it may be different, which is
    the case when further substitutions are made within a substitution.

- [function] MAKE-SUB VAR SUBFORM NEW-FORM VALUESP

- [structure-accessor] SUB-VAR SUB

- [structure-accessor] SUB-SUBFORM SUB

- [structure-accessor] SUB-NEW-FORM SUB

- [structure-accessor] SUB-VALUESP SUB

- [generic-function] SUBSTITUTE-IS-LIST-FORM FIRST FORM ENV

    In the list FORM, whose CAR is FIRST, substitute
    subexpressions of interest with a GENSYM and return the new form. As
    the second value, return a list of SUBs.
    
    For example, consider `(IS (FIND (FOO) LIST))`. When
    SUBSTITUTE-IS-LIST-FORM is invoked on `(FIND (FOO) LIST)`, it
    substitutes each argument of FIND with a variable, returning the new
    form `(FIND TEMP1 TEMP2)` and the list of two
    substitutions `((TEMP2 (FOO) (FOO) NIL) (TEMP3 LIST LIST NIL))`.
    This allows the original form to be rewritten as
    
    ```
    (let* ((temp1 (foo))
           (temp2 list))
      (find temp1 temp2))
    ```
    
    TEMP1 and TEMP2 may then be reported in the OUTCOME condition
    signalled by IS like this:
    
        The following check failed:
          (is (find #1=(foo) #2=list))
        where
          #1# = <return-value-of-foo>
          #2# = <value-of-variable-list>


#### Explicit Captures

In addition to automatic captures, which are prescribed by
rewriting rules (see @TRY/WRITING-AUTOMATIC-CAPTURE-RULES),
explicit, ad-hoc captures can also be made.

```common-lisp
(is (let ((x 1))
      (= (capture x) 2)))
.. debugger invoked on UNEXPECTED-RESULT-FAILURE:
..   UNEXPECTED-FAILURE in check:
..     (IS
..      (LET ((X 1))
..        (= (CAPTURE X) 2)))
..   where
..     X = 1
```

If CAPTURE showing up in the form that IS prints is undesirable,
then `%` may be used instead:

```common-lisp
(is (let ((x 1))
      (= (% x) 2)))
.. debugger invoked on UNEXPECTED-RESULT-FAILURE:
..   UNEXPECTED-FAILURE in check:
..     (IS
..      (LET ((X 1))
..        (= X 2)))
..   where
..     X = 1
```

Multiple values may be captured with CAPTURE-VALUES and its
secretive counterpart `%%`:

```common-lisp
(is (= (%% (values 1 2)) 2))
.. debugger invoked on UNEXPECTED-RESULT-FAILURE:
..   UNEXPECTED-FAILURE in check:
..     (IS (= #1=(VALUES 1 2) 2))
..   where
..     #1# == 1
..            2
```

where printing `==` instead of = indicates that this
is a multiple value capture.

- [macro] CAPTURE FORM

    Evaluate FORM, record its primary return value if within the
    dynamic extent of an IS evaluation, and finally return that value.
    If CAPTURE is used within the lexical scope of IS, then CAPTURE
    itself will show up in the form that the default MSG prints. Thus it
    is recommended to use the equivalent MACROLET `%` in the lexical
    scope as `%` is removed before printing.

- [macro] CAPTURE-VALUES FORM

    Like CAPTURE-VALUES, but record and return all values returned by
    FORM. It is recommended to use the equivalent MACROLET `%%` in the
    lexical scope as `%%` is removed before printing.

- [macrolet] % FORM

    An alias for CAPTURE in the lexical scope of IS. Removed from the
    IS form when printed.

- [macrolet] %% FORM

    An alias for CAPTURE-VALUES in the lexical scope of IS. Removed
    from the IS form when printed.

## Check Library

In the following, various checks built on top of IS are described.
Many of them share a number of arguments, which are described here.

- ON-RETURN is a boolean that determines whether the check in a
  macro that wraps BODY is made when BODY returns normally.

- ON-NLX is a boolean that determines whether the check in a macro
  that wraps BODY is made when BODY performs a non-local exit.

- MSG and CTX are @TRY/FORMAT-SPECIFIER-FORMS as in IS.

- NAME may be provided so that it is printed (with PRIN1) instead of
  BODY in MSG.


### Checking Conditions

The macros SIGNALS, SIGNALS-NOT, INVOKES-DEBUGGER, and
INVOKES-DEBUGGER-NOT all check whether a condition of a given type,
possibly also matching a predicate, was signalled. In addition to
those already described in @TRY/CHECK-LIBRARY, these macros share a
number of arguments.

Matching conditions are those that are of type CONDITION-TYPE (not
evaluated) and satisfy the predicate PRED.

When PRED is NIL, it always matches. When it is a string, then it
matches if it is a substring of the printed representation of the
condition being handled (by PRINC under WITH-STANDARD-IO-SYNTAX).
When it is a function, it matches if it returns true when called
with the condition as its argument.

The check is performed in the cleanup form of an UNWIND-PROTECT
around BODY.

HANDLER is called when a matching condition is found. It can be a
function, T, or NIL. When it is a function, it is called from the
condition handler (SIGNALS and SIGNALS-NOT) or the debugger
hook (invokes-debugger and INVOKES-DEBUGGER-NOT) with the matching
condition. HANDLER may perform a non-local exit. When HANDLER is T,
the matching condition is handled by performing a non-local exit to
just outside BODY. If the exit completes, BODY is treated as if it
had returned normally, and ON-RETURN is consulted. When HANDLER is
NIL, no addition action is performed when a matching condition is
found.

The default CTX describes the result of the matching process in
terms of *CONDITION-MATCHED-P* and *BEST-MATCHING-CONDITION*.

- [variable] *CONDITION-MATCHED-P*

    When a check described in @TRY/CHECKING-CONDITIONS signals its
    OUTCOME, this variable is bound to a boolean value to indicate
    whether a condition that matched CONDITION-TYPE and PRED was
    found.

- [variable] *BEST-MATCHING-CONDITION*

    Bound when a check described in @TRY/CHECKING-CONDITIONS
    signals its OUTCOME. If *CONDITION-MATCHED-P*, then it is the
    most recent condition that matched both CONDITION-TYPE and PRED.
    Else, it is the most recent condition that matched
    CONDITION-TYPE or NIL if no such conditions were detected.

- [macro] SIGNALS (CONDITION-TYPE &KEY PRED (HANDLER T) (ON-RETURN T) (ON-NLX T) NAME MSG CTX) &BODY BODY

    Check that BODY signals a CONDITION of CONDITION-TYPE (not
    evaluated) that matches PRED. To detect matching conditions, SIGNALS
    sets up a HANDLER-BIND. Thus it can only see what BODY does not
    handle. The arguments are described in @TRY/CHECKING-CONDITIONS.
    
    ```common-lisp
    (signals (error)
      (error "xxx"))
    => NIL
    ```
    
    The following example shows a failure where CONDITION-TYPE matches
    but PRED does not.
    
    ```common-lisp
    (signals (error :pred "non-matching")
      (error "xxx"))
    .. debugger invoked on UNEXPECTED-RESULT-FAILURE:
    ..   UNEXPECTED-FAILURE in check:
    ..     (ERROR "xxx") signals a condition of type ERROR that matches
    ..     "non-matching".
    ..   The predicate did not match "xxx".
    ```


- [macro] SIGNALS-NOT (CONDITION-TYPE &KEY PRED (HANDLER T) (ON-RETURN T) (ON-NLX T) NAME MSG CTX) &BODY BODY

    Check that BODY does not signal a CONDITION of CONDITION-TYPE (not
    evaluated) that matches PRED. To detect matching conditions,
    SIGNALS-NOT sets up a HANDLER-BIND. Thus, it can only see what BODY
    does not handle. The arguments are described in
    @TRY/CHECKING-CONDITIONS.

- [macro] INVOKES-DEBUGGER (CONDITION-TYPE &KEY PRED (HANDLER T) (ON-RETURN T) (ON-NLX T) NAME MSG CTX) &BODY BODY

    Check that BODY enters the debugger with a CONDITION of
    CONDITION-TYPE (not evaluated) that matches PRED. To detect matching
    conditions, INVOKES-DEBUGGER sets up a *DEBUGGER-HOOK*. Thus, if
    *DEBUGGER-HOOK* is changed by BODY, it may not detect the condition.
    The arguments are described in @TRY/CHECKING-CONDITIONS.
    
    Note that in a trial (see CURRENT-TRIAL), all ERRORs are handled,
    and a *DEBUGGER-HOOK* is set up (see UNHANDLED-ERROR). Thus,
    invoking debugger would normally cause the trial to abort.
    
    ```common-lisp
    (invokes-debugger (error :pred "xxx")
      (handler-bind ((error #'invoke-debugger))
        (error "xxx")))
    => NIL
    ```


- [macro] INVOKES-DEBUGGER-NOT (CONDITION-TYPE &KEY PRED (HANDLER T) (ON-RETURN T) (ON-NLX T) NAME MSG CTX) &BODY BODY

    Check that BODY does not enter the debugger with a CONDITION of
    CONDITION-TYPE (not evaluated) that matches PRED. To detect matching
    conditions, INVOKES-DEBUGGER-NOT sets up a *DEBUGGER-HOOK*. Thus, if
    *DEBUGGER-HOOK* is changed by BODY, it may not detect the condition.
    The arguments are described in @TRY/CHECKING-CONDITIONS.

### Miscellaneous Checks

- [macro] FAILS (&KEY NAME MSG CTX) &BODY BODY

    Check that BODY performs a non-local exit but do not
    cancel it (see @CANCELLED-NLX). See @TRY/CHECK-LIBRARY for the
    descriptions of the other arguments.
    
    In the following example, FAILS signals a SUCCESS.
    
    ```common-lisp
    (catch 'foo
      (fails ()
        (throw 'foo 7)))
    => 7
    ```
    
    Next, FAILS signals an UNEXPECTED-FAILURE because BODY returns
    normally.
    
    ```common-lisp
    (fails ()
      (print 'hey))
    ..
    .. HEY 
    .. debugger invoked on UNEXPECTED-RESULT-FAILURE:
    ..   UNEXPECTED-FAILURE in check:
    ..     (PRINT 'HEY) does not return normally.
    ```
    
    Note that there is no `FAILS-NOT` as WITH-TEST fills that role.

- [macro] IN-TIME (SECONDS &KEY (ON-RETURN T) (ON-NLX T) NAME MSG CTX) &BODY BODY

    Check that BODY finishes in SECONDS. See @TRY/CHECK-LIBRARY for
    the descriptions of the other arguments.
    
    ```
    (in-time (1)
      (sleep 2))
    .. debugger invoked on UNEXPECTED-RESULT-FAILURE:
    ..   UNEXPECTED-FAILURE in check:
    ..     (SLEEP 2) finishes within 1s.
    ..   Took 2.000s.
    ```
    
    RETRY-CHECK restarts timing.

- [variable] *IN-TIME-ELAPSED-SECONDS*

    Bound to the number of seconds passed during the evaluation of
    BODY when IN-TIME signals its OUTCOME.

### Check Utilities

These utilities are not checks (which signal OUTCOMEs) but simple
functions and macros that may be useful for writing IS checks.

- [macro] ON-VALUES FORM &BODY BODY

    ON-VALUES evaluates FORM and transforms its return values one by
    one based on forms in BODY. The Nth value is replaced by the return
    value of the Nth form of BODY evaluated with `*` bound
    to the Nth value. If the number of values exceeds the number of
    transformation forms in BODY then the excess values are returned as
    is.
    
    ```common-lisp
    (on-values (values 1 "abc" 7)
      (1+ *)
      (length *))
    => 2
    => 3
    => 7
    ```
    
    If the number of values is less than the number of transformation
    forms, then in later transformation forms `*` is bound
    to NIL.
    
    ```common-lisp
    (on-values (values)
      *
      *)
    => NIL
    => NIL
    ```
    
    The first forms in BODY may be options. Options must precede
    transformation forms. With :TRUNCATE T, the excess values are
    discarded.
    
    ```common-lisp
    (on-values (values 1 "abc" 7)
      (:truncate t)
      (1+ *)
      (length *))
    => 2
    => 3
    ```
    
    The :ON-LENGTH-MISMATCH option may be NIL or a function of a single
    argument. If the number of values and the number of transformation
    forms are different, then this function is called to transform the
    list of values. :TRUNCATE is handled before :ON-LENGTH-MISMATCH.
    
    ```common-lisp
    (on-values 1
      (:on-length-mismatch (lambda (values)
                             (if (= (length values) 1)
                                 (append values '("abc"))
                                 values)))
      (1+ *)
      *)
    => 2
    => "abc"
    ```
    
    If the same option is specified multiple times, the first one is in
    effect.

- [macro] MATCH-VALUES FORM &BODY BODY

    MATCH-VALUES returns true iff all return values of FORM satisfy
    the predicates given by BODY, which are described in ON-VALUES. The
    :TRUNCATE option of ON-VALUES is supported, but :ON-LENGTH-MISMATCH
    always returns NIL.
    
    ```common-lisp
    ;; no values
    (is (match-values (values)))
    ;; single value success
    (is (match-values 1
          (= * 1)))
    ;; success with different types
    (is (match-values (values 1 "sdf")
          (= * 1)
          (string= * "sdf")))
    ;; too few values
    (is (not (match-values 1
               (= * 1)
               (string= * "sdf"))))
    ;; too many values
    (is (not (match-values (values 1 "sdf" 3)
               (= * 1)
               (string= * "sdf"))))
    ;; too many values, but truncated
    (is (match-values (values 1 "sdf" 3)
          (:truncate t)
          (= * 1)
          (string= * "sdf")))
    ```


- [function] MISMATCH% SEQUENCE1 SEQUENCE2 &KEY FROM-END (TEST \#'EQL) (START1 0) END1 (START2 0) END2 KEY MAX-PREFIX-LENGTH MAX-SUFFIX-LENGTH

    Like CL:MISMATCH but CAPTUREs and returns the common prefix and
    the mismatched suffixes. The `TEST-NOT` argument is deprecated by
    the CLHS and is not supported. In addition, if MAX-PREFIX-LENGTH and
    MAX-SUFFIX-LENGTH are non-`NIL`, they must be non-negative integers,
    and they limit the number of elements in the prefix and the
    suffixes.
    
    ```common-lisp
    (is (null (mismatch% '(1 2 3) '(1 2 4 5))))
    .. debugger invoked on UNEXPECTED-RESULT-FAILURE:
    ..   UNEXPECTED-FAILURE in check:
    ..     (IS (NULL #1=(MISMATCH% '(1 2 3) '(1 2 4 5))))
    ..   where
    ..     COMMON-PREFIX = (1 2)
    ..     MISMATCHED-SUFFIX-1 = (3)
    ..     MISMATCHED-SUFFIX-2 = (4 5)
    ..     #1# = 2
    ```
    
    ```common-lisp
    (is (null (mismatch% "Hello, World!"
                         "Hello, world!")))
    .. debugger invoked on UNEXPECTED-RESULT-FAILURE:
    ..   UNEXPECTED-FAILURE in check:
    ..     (IS (NULL #1=(MISMATCH% "Hello, World!" "Hello, world!")))
    ..   where
    ..     COMMON-PREFIX = "Hello, "
    ..     MISMATCHED-SUFFIX-1 = "World!"
    ..     MISMATCHED-SUFFIX-2 = "world!"
    ..     #1# = 7
    ```


- [function] DIFFERENT-ELEMENTS SEQUENCE1 SEQUENCE2 &KEY (PRED \#'EQL) (MISSING :MISSING)

    Return the different elements under PRED in the given sequences as
    a list of `(:INDEX <INDEX> <E1> <E2>)` elements, where `E1` and `E2`
    are elements of SEQUENCE1 and SEQUENCE2 at `<INDEX>`, respectively,
    and they may be MISSING if the corresponding sequence is too short.
    
    ```common-lisp
    (is (endp (different-elements '(1 2 3) '(1 b 3 d))))
    .. debugger invoked on UNEXPECTED-RESULT-FAILURE:
    ..   UNEXPECTED-FAILURE in check:
    ..     (IS (ENDP #1=(DIFFERENT-ELEMENTS '(1 2 3) '(1 B 3 D))))
    ..   where
    ..     #1# = ((:INDEX 1 2 B) (:INDEX 3 :MISSING D))
    ```


- [function] SAME-SET-P LIST1 LIST2 &KEY KEY (TEST \#'EQL)

    See if LIST1 and LIST2 represent the same set.
    See CL:SET-DIFFERENCE for a description of the KEY and TEST arguments.

- [macro] WITH-SHUFFLING NIL &BODY BODY

    Execute the forms that make up the list of forms BODY in random
    order and return NIL. This may be useful to prevent writing tests
    that accidentally depend on the order in which subtests are called.
    
    ```common-lisp
    (loop repeat 3 do
      (with-shuffling ()
        (prin1 1)
        (prin1 2)))
    .. 122112
    => NIL
    ```


#### Comparing Floats

Float comparisons following
[https://randomascii.wordpress.com/2012/02/25/comparing-floating-point-numbers-2012-edition/](https://randomascii.wordpress.com/2012/02/25/comparing-floating-point-numbers-2012-edition/).

- [function] FLOAT-~= X Y &KEY (MAX-DIFF-IN-VALUE \*MAX-DIFF-IN-VALUE\*) (MAX-DIFF-IN-ULP \*MAX-DIFF-IN-ULP\*)

    Return whether two numbers, X and Y, are approximately equal either
    according to MAX-DIFF-IN-VALUE or MAX-DIFF-IN-ULP.
    
    If the absolute value of the difference of two floats is not greater
    than MAX-DIFF-IN-VALUE, then they are considered equal.
    
    If two floats are of the same sign and the number of representable
    floats (ULP, unit in the last place) between them is less than
    MAX-DIFF-IN-ULP, then they are considered equal.
    
    If neither X nor Y are floats, then the comparison is done with `=`.
    If one of them is a DOUBLE-FLOAT, then the other is converted to a
    double float, and the comparison takes place in double float space.
    Else, both are converted to SINGLE-FLOAT and the comparison takes
    place in single float space.

- [variable] *MAX-DIFF-IN-VALUE* 1.0e-16

    The default value of the MAX-DIFF-IN-VALUE argument of FLOAT-~=.

- [variable] *MAX-DIFF-IN-ULP* 2

    The default value of the MAX-DIFF-IN-ULP argument of FLOAT-~=.

- [function] FLOAT-~< X Y &KEY (MAX-DIFF-IN-VALUE \*MAX-DIFF-IN-VALUE\*) (MAX-DIFF-IN-ULP \*MAX-DIFF-IN-ULP\*)

    Return whether X is approximately less than Y. Equivalent to `<`,
    but it also allows for approximate equality according to FLOAT-~=.

- [function] FLOAT-~> X Y &KEY (MAX-DIFF-IN-VALUE \*MAX-DIFF-IN-VALUE\*) (MAX-DIFF-IN-ULP \*MAX-DIFF-IN-ULP\*)

    Return whether X is approximately greater than Y. Equivalent to `>`,
    but it also allows for approximate equality according to FLOAT-~=.

## Tests

In Try, tests are Lisp functions that record their execution in
TRIAL objects. TRIALs are to tests what function call traces are to
functions. In more detail, tests

- create a TRIAL object and signal a TRIAL-START event upon entry to
  the function,

- signal a VERDICT condition before returning normally or via a
  non-local exit,

- return the TRIAL object as the first value,

- return explicitly returned values as the second, third, and so on
  values.

See DEFTEST and WITH-TEST for more precise descriptions.

- [macro] DEFTEST NAME LAMBDA-LIST &BODY BODY

    DEFTEST is a wrapper around DEFUN to define global test functions.
    See DEFUN for a description of NAME, LAMBDA-LIST, and BODY. The
    behaviour common with WITH-TEST is described in @TRY/TESTS.
    
    ```common-lisp
    (deftest my-test ()
      (write-string "hey"))
    => MY-TEST
    
    (test-bound-p 'my-test)
    => T
    
    (my-test)
    .. hey
    ==> #<TRIAL (MY-TEST) EXPECTED-SUCCESS 0.000s>
    ```
    
    Although the common case is for tests to have no arguments, DEFTEST
    supports general function lambda lists. Within a global test,
    
    - NAME is bound to the TRIAL object
    
    - the first return value is the trial
    
    - values are not returned implicitly
    
    - values returned with an explicit RETURN-FROM are returned as
      values after the trial
    
    ```common-lisp
    (deftest my-test ()
      (prin1 my-test)
      (return-from my-test (values 2 3)))
    
    (my-test)
    .. #<TRIAL (MY-TEST) RUNNING>
    ==> #<TRIAL (MY-TEST) EXPECTED-SUCCESS 0.000s>
    => 2
    => 3
    ```


- [variable] *RUN-DEFTEST-WHEN* NIL

    This may be any of :COMPILE-TOPLEVEL, :LOAD-TOPLEVEL, :EXECUTE, or
    a list thereof. The value of *RUN-DEFTEST-WHEN* determines in what
    EVAL-WHEN situation to call the test function immediately after it
    has been defined with DEFTEST.
    
    For interactive development, it may be convenient to set it to
    :EXECUTE and have the test run when the DEFTEST is evaluated (maybe
    with Slime `C-M-x`, `slime-eval-defun`). Or set it to
    :COMPILE-TOPLEVEL, and have it rerun on Slime `C-c C-c`,
    `slime-compile-defun`.
    
    If the test has required arguments, an argument list is prompted for
    and read from *QUERY-IO*.

- [function] TEST-BOUND-P SYMBOL

    See if SYMBOL names a global test (i.e. a test defined with
    DEFTEST). If since the execution of DEFTEST, the symbol has been
    UNINTERNed, FMAKUNBOUNDed, or redefined with DEFUN, then it no
    longer names a global test.

- [macro] WITH-TEST (&OPTIONAL TRIAL-VAR &KEY NAME) &BODY BODY

    Define a so-called lambda test to group together CHECKs and other
    tests it executes. WITH-TEST executes BODY in its lexical
    environment even on a rerun (see @TRY/RERUN).
    
    If TRIAL-VAR is a non-`NIL` symbol, bind it to the trial object.
    NAME may be any type, it is purely for presentation purposes. If
    NAME is NIL, then it defaults to TRIAL-VAR.
    
    To facilitate returning values, a BLOCK is wrapped around BODY. The
    name of the block is TRIAL-VAR if it is a symbol, else it's NIL.
    
    When both TRIAL-VAR and NAME are specified:
    
    ```common-lisp
    (with-test (some-feature :name "obscure feature")
      (prin1 some-feature)
      (is t)
      (return-from some-feature (values 1 2)))
    .. #<TRIAL (WITH-TEST ("obscure feature")) RUNNING>
    .. obscure feature
    ..   ⋅ (IS T)
    .. ⋅ obscure feature ⋅1
    ..
    ==> #<TRIAL (WITH-TEST ("obscure feature")) EXPECTED-SUCCESS 0.002s ⋅1>
    => 1
    => 2
    ```
    
    If only TRIAL-VAR is specified:
    
    ```common-lisp
    (with-test (some-feature)
      (prin1 some-feature)
      (is t)
      (return-from some-feature (values 1 2)))
    .. #<TRIAL (WITH-TEST (SOME-FEATURE)) RUNNING>
    .. SOME-FEATURE
    ..   ⋅ (IS T)
    .. ⋅ SOME-FEATURE ⋅1
    ..
    ==> #<TRIAL (WITH-TEST (SOME-FEATURE)) EXPECTED-SUCCESS 0.000s ⋅1>
    => 1
    => 2
    ```
    
    If neither is specified:
    
    ```common-lisp
    (with-test ()
      (prin1 (current-trial))
      (is t)
      (return (values 1 2)))
    .. #<TRIAL (WITH-TEST (NIL)) RUNNING>
    .. NIL
    ..   ⋅ (IS T)
    .. ⋅ NIL ⋅1
    ..
    ==> #<TRIAL (WITH-TEST (NIL)) EXPECTED-SUCCESS 0.000s ⋅1>
    => 1
    => 2
    ```
    
    Finally, using that NAME defaults to TRIAL-VAR and that it is valid
    to specify non-symbols for TRIAL-VAR, one can also write:
    
    ```common-lisp
    (with-test ("Some feature")
      (prin1 (current-trial))
      (is t)
      (return (values 1 2)))
    .. #<TRIAL (WITH-TEST ("Some feature")) RUNNING>
    .. Some feature
    ..   ⋅ (IS T)
    .. ⋅ Some feature ⋅1
    ..
    ==> #<TRIAL (WITH-TEST ("Some feature")) EXPECTED-SUCCESS 0.000s ⋅1>
    => 1
    => 2
    ```
    
    In summary and in contrast to global tests (those defined with
    DEFTEST), lambda tests
    
    - have no arguments,
    
    - are defined and called at the same time,
    
    - may not bind their trial object to any variable,
    
    - may have a BLOCK named NIL,
    
    - have a NAME purely for presentation purposes.
    
    Lambda tests can be thought of as analogous to `(FUNCALL (LAMBDA ()
    BODY))`. The presence of the LAMBDA is important because it is
    stored in the TRIAL object to support @TRY/RERUN.

- [function] LIST-PACKAGE-TESTS &OPTIONAL (PACKAGE \*PACKAGE\*)

    List all symbols in PACKAGE that name global tests in the sense of
    TEST-BOUND-P.

- [macro] WITH-TESTS-RUN (TESTS-RUN) &BODY BODY

    Bind the symbol TESTS-RUN to an empty `EQ` hash table and execute
    BODY. The has table reflects call counts to global tests. Keys are
    symbols naming global tests, and the values are the number of times
    the keys have been called.

- [macro] WARN-ON-TESTS-NOT-RUN (&OPTIONAL (PACKAGE \*PACKAGE\*)) &BODY BODY

    A convenience utility to that records the global tests run by BODY
    with WITH-TESTS-RUN and, when BODY finishes, signals a warning for
    each global tests in PACKAGE not run.
    
    This is how Try runs its own tests:
    
    ```
    (defun test ()
      ;; Bind *PACKAGE* so that names of tests printed have package names,
      ;; and M-. works on them in Slime.
      (let ((*package* (find-package :common-lisp)))
        (warn-on-tests-not-run ((find-package :try))
          (print (try 'test-all
                      :print 'unexpected
                      :describe 'unexpected)))))
    ```


### Calling Test Functions

Tests can be run explicitly by invoking the TRY function or
implicitly by calling a test function:

```common-lisp
(deftest my-test ()
  (is t))

(my-test)
.. MY-TEST
..   ⋅ (IS T)
.. ⋅ MY-TEST ⋅1
..
==> #<TRIAL (MY-TEST) EXPECTED-SUCCESS 0.004s ⋅1>
```

The situation is similar with a WITH-TEST:

```common-lisp
(with-test (my-test)
  (is t))
.. MY-TEST
..   ⋅ (IS T)
.. ⋅ MY-TEST ⋅1
..
==> #<TRIAL (WITH-TEST (MY-TEST)) EXPECTED-SUCCESS 0.000s ⋅1>
```

Behind the scenes, the outermost test function calls TRY with

```
(try trial :debug *debug* :collect *collect* :rerun *rerun*
     :print *print* :describe *describe*
     :stream *stream* :printer *printer*)
```

TRY then calls the test function belonging to TRIAL.
The rest of the behaviour is described in @TRY/EXPLICIT-TRY.

- [variable] *DEBUG* (AND UNEXPECTED (NOT NLX) (NOT VERDICT))

    The default value makes TRY invoke the debugger on UNHANDLED-ERROR,
    RESULT-ABORT\*, UNEXPECTED-RESULT-FAILURE, and
    UNEXPECTED-RESULT-SUCCESS. NLX is excluded because it is caught as
    the test function is being exited, but by that time the dynamic
    environment of the actual cause is likely gone. VERDICT is excluded
    because it is a consequence of its child outcomes.

- [variable] *COUNT* LEAF

    Although the default value of *CATEGORIES* lumps RESULTs and
    VERDICTs together, with the default of LEAF, VERDICTs are not
    counted. See @TRY/COUNT.

- [variable] *COLLECT* UNEXPECTED

    To save memory, only the UNEXPECTED are collected by default.
    See @TRY/COLLECT.

- [variable] *RERUN* UNEXPECTED

    The default matches that of *COLLECT*. See @TRY/RERUN.

- [variable] *PRINT* LEAF

    With the default of LEAF combined with the default *PRINT-PARENT*
    T, only TRIALs with checks or ERROR\* in them are printed. If
    UNEXPECTED, only the interesting things are printed. See @TRY/PRINT.

- [variable] *DESCRIBE* (OR UNEXPECTED FAILURE)

    By default, the context (e.g. @TRY/CAPTURES, and the CTX argument
    of is and other checks) of UNEXPECTED events is described. See
    @TRY/PRINT.

- [variable] *STREAM* (MAKE-SYNONYM-STREAM '\*DEBUG-IO\*)

- [variable] *PRINTER* TREE-PRINTER

### Explicit TRY

Instead of invoking the test function directly, tests can also be
run by invoking the TRY function.

```common-lisp
(deftest my-test ()
  (is t))

(try 'my-test)
.. MY-TEST
..   ⋅ (IS T)
.. ⋅ MY-TEST ⋅1
..
==> #<TRIAL (MY-TEST) EXPECTED-SUCCESS 0.000s ⋅1>
```

The situation is similar with a WITH-TEST, only that TRY wraps an
extra TRIAL around the execution of the LAMBDA to ensure that all
EVENTs are signalled within a trial.

```
(try (lambda ()
       (with-test (my-test)
         (is t))))
.. (TRY #<FUNCTION (LAMBDA ()) {531FE50B}>)
..   MY-TEST
..     ⋅ (IS T)
..   ⋅ MY-TEST ⋅1
.. ⋅ (TRY #<FUNCTION (LAMBDA ()) {531FE50B}>) ⋅1
..
==> #<TRIAL (TRY #<FUNCTION (LAMBDA ()) {531FE50B}>) EXPECTED-SUCCESS 0.000s ⋅1>
```

Invoking tests with an explicit TRY is very similar to just calling
the test functions directly (see @TRY/IMPLICIT-TRY). The differences
are that TRY

- can run @TRY/TESTABLES,

- has a function argument for each of the *DEBUG*, *COLLECT*, etc
  variables.

Those arguments default to *TRY-DEBUG*, *TRY-COLLECT*, etc, which
parallel and default to *DEBUG*, *COLLECT*, etc if set to
:UNSPECIFIED. *TRY-DEBUG* is NIL, the rest of them are :UNSPECIFIED.

These defaults encourage the use of an explicit TRY call in the
non-interactive case and calling the test functions directly in the
interactive one, but this is not enforced in any way.

- [function] TRY TESTABLE &KEY (DEBUG \*TRY-DEBUG\*) (COUNT \*TRY-COUNT\*) (COLLECT \*TRY-COLLECT\*) (RERUN \*TRY-RERUN\*) (PRINT \*TRY-PRINT\*) (DESCRIBE \*TRY-DESCRIBE\*) (STREAM \*TRY-STREAM\*) (PRINTER \*TRY-PRINTER\*)

    TRY runs TESTABLE and handles the EVENTs to collect, debug, print
    the results of checks and trials, and to decide what tests to skip
    and what to rerun.
    
    DEBUG, COUNT, COLLECT, RERUN, PRINT, and DESCRIBE must all be valid
    specifiers for types that are either NIL (the empty type) or have a
    non-empty intersection with the type EVENT (e.g. T, OUTCOME,
    UNEXPECTED, VERDICT).
    
    TRY sets up a HANDLER-BIND handler for EVENTs and runs TESTABLE (see
    @TRY/TESTABLES). When an EVENT is signalled, the handler matches its
    type to the value of the DEBUG argument (in the sense of `(TYPEP
    EVENT DEBUG)`). If it matches, then the debugger is invoked with the
    event. In the debugger, the user has a number of restarts available
    to change (see @TRY/EVENT-RESTARTS, @TRY/OUTCOME-RESTARTS,
    @TRY/CHECK-RESTARTS, @TRY/TRIAL-RESTARTS, and SET-TRY-DEBUG.
    
    If the debugger is not invoked, TRY invokes the very first restart
    available, which is always RECORD-EVENT.
    
    Recording the event is performed as follows.
    
    - Outcome counts are updated (see @TRY/COUNT).
    
    - The event is passed to the collector (see @TRY/COLLECT).
    
    - The event is passed to the printer (see @TRY/PRINT).
    
    - Finally, when rerunning a trial (i.e. when TESTABLE is a trial),
      on a TRIAL-START event, the trial may be skipped (see @TRY/RERUN).
    
    TRY returns the values returned by the outermost trial (see
    @TRY/TESTS).

- [function] SET-TRY-DEBUG DEBUG

    Invoke the SET-TRY-DEBUG restart to override the DEBUG argument of
    the currently running TRY. DEBUG must thus be a suitable type. When
    the SET-TRY-DEBUG restart is invoked interactively, DEBUG is read as
    a non-evaluated form from *QUERY-IO*.

- [variable] *TRY-DEBUG* NIL

    The default value for TRY's :DEBUG argument. If
    :UNSPECIFIED, then the value of *DEBUG* is used instead.

- [variable] *TRY-COUNT* :UNSPECIFIED

    The default value for TRY's :COUNT argument. If
    :UNSPECIFIED, then the value of *COUNT* is used instead.

- [variable] *TRY-COLLECT* :UNSPECIFIED

    The default value for TRY's :COLLECT argument. If
    :UNSPECIFIED, then the value of *COLLECT* is used instead.

- [variable] *TRY-RERUN* :UNSPECIFIED

    The default value for TRY's :RERUN argument. If
    :UNSPECIFIED, then the value of *RERUN* is used instead.

- [variable] *TRY-PRINT* :UNSPECIFIED

    The default value for TRY's :PRINT argument. If
    :UNSPECIFIED, then the value of *PRINT* is used instead.

- [variable] *TRY-DESCRIBE* :UNSPECIFIED

    The default value for TRY's :DESCRIBE argument. If
    :UNSPECIFIED, then the value of *DESCRIBE* is used instead.

- [variable] *TRY-STREAM* :UNSPECIFIED

    The default value for TRY's :STREAM argument. If
    :UNSPECIFIED, then the value of *STREAM* is used instead.

- [variable] *TRY-PRINTER* :UNSPECIFIED

    The default value for TRY's :PRINTER argument. If
    :UNSPECIFIED, then the value of *PRINTER* is used instead.

- [variable] *N-RECENT-TRIALS* 3

    See *RECENT-TRIALS*.

- [function] RECENT-TRIAL &OPTIONAL (N 0)

    Returns the `N`th most recent trial or NIL if there are not enough
    trials recorded. Every TRIAL returned by TRY gets pushed
    onto a list of trials, but only *N-RECENT-TRIALS* are kept.

- [variable] ! NIL

    The most recent trial. Equivalent to `(RECENT-TRIAL 0)`.

- [variable] !! NIL

    Equivalent to `(RECENT-TRIAL 1)`.

- [variable] !!! NIL

    Equivalent to `(RECENT-TRIAL 2)`.

#### Testables

Valid first arguments to TRY are called testables. A testable may
be:

- a function designator

    - the name of a global test

    - the name of a global function

    - a function object

    - a trial

- a list of testables

- a PACKAGE

In the function designator cases, TRY calls the designated function.
TRIALs, being @FUNCALLABLE-INSTANCEs, designate themselves. If the
trial is not RUNNINGP, then it will be rerun (see @TRY/RERUN). Don't
invoke TRY with RUNNINGP trials (but see
@TRY/IMPLICIT-TRY-IMPLEMENTATION for discussion).

When given a list of testables, TRY calls each testable one by one.

Finally, a PACKAGE stands for the result of calling
LIST-PACKAGE-TESTS on that package.

#### Implementation of Implicit TRY

What's happening in the implementation is that a test function,
when it is called, checks whether it is running under the TRY
function. If it isn't, then it invokes TRY with its TRIAL. TRY
realizes the trial cannot be rerun yet (see @TRY/RERUN) because it
is RUNNINGP, sets up its event handlers for debugging, collecting,
printing, and invokes the trial as if it were rerun but without
skipping anything based on the RERUN argument. Thus the following
are infinite recursions:

```
(with-test (recurse)
  (try recurse))

(with-test (recurse)
  (funcall recurse))
```


### Printing Events

TRY instantiates a printer of the type given by its PRINTER
argument. All EVENTs recorded by TRY are sent to this printer. The
printer then prints events that match the type given by the PRINT
argument of TRY. Events that also match the DESCRIBE argument of TRY
are printed with context information (see IS) and backtraces (see
UNHANDLED-ERROR).

Although the printing is primarily customized with global special
variables, changing the value of those variables after the printer
object is instantiated by TRY has no effect. This is to ensure
consistent output with nested TRY calls of differing printer
setups.

- [class] TREE-PRINTER

    TREE-PRINTER prints events in an indented
    tree-like structure, with each internal node corresponding to a
    TRIAL. This is the default printer (according to *PRINTER* and
    *TRY-PRINTER*) and currently the only one.
    
    The following example prints all @TRY/CONCRETE-EVENTS.
    
    ```common-lisp
    (let ((*debug* nil)
          (*print* '(not trial-start))
          (*describe* nil))
      (with-test (verdict-abort*)
        (with-test (expected-verdict-success))
        (with-expected-outcome ('failure)
          (with-test (unexpected-verdict-success)))
        (handler-bind (((and verdict success) #'force-expected-failure))
          (with-test (expected-verdict-failure)))
        (handler-bind (((and verdict success) #'force-unexpected-failure))
          (with-test (unexpected-verdict-failure)))
        (with-test (verdict-skip)
          (skip-trial))
        (is t :msg "EXPECTED-RESULT-SUCCESS")
        (with-failure-expected ('failure)
          (is t :msg "UNEXPECTED-RESULT-SUCCESS")
          (is nil :msg "EXPECTED-RESULT-FAILURE"))
        (is nil :msg "UNEXPECTED-RESULT-FAILURE")
        (with-skip ()
          (is nil :msg "RESULT-SKIP"))
        (handler-bind (((and result success) #'abort-check))
          (is t :msg "RESULT-ABORT*"))
        (catch 'foo
          (with-test (nlx-test)
            (throw 'foo nil)))
        (error "UNHANDLED-ERROR")))
    .. VERDICT-ABORT*                       ; TRIAL-START
    ..   ⋅ EXPECTED-VERDICT-SUCCESS
    ..   ⊡ UNEXPECTED-VERDICT-SUCCESS
    ..   × EXPECTED-VERDICT-FAILURE
    ..   ⊠ UNEXPECTED-VERDICT-FAILURE
    ..   - VERDICT-SKIP
    ..   ⋅ EXPECTED-RESULT-SUCCESS
    ..   ⊡ UNEXPECTED-RESULT-SUCCESS
    ..   × EXPECTED-RESULT-FAILURE
    ..   ⊠ UNEXPECTED-RESULT-FAILURE
    ..   - RESULT-SKIP
    ..   ⊟ RESULT-ABORT*
    ..   NLX-TEST                           ; TRIAL-START
    ..     ⊟ non-local exit                 ; NLX
    ..   ⊟ NLX-TEST ⊟1                      ; VERDICT-ABORT*
    ..   ⊟ "UNHANDLED-ERROR" (SIMPLE-ERROR)
    .. ⊟ VERDICT-ABORT* ⊟3 ⊠1 ⊡1 -1 ×1 ⋅1
    ..
    ==> #<TRIAL (WITH-TEST (VERDICT-ABORT*)) ABORT* 0.004s ⊟3 ⊠1 ⊡1 -1 ×1 ⋅1>
    ```
    
    The `⊟3 ⊠1 ⊡1 -1 ×1 ⋅1` part is the counts for *CATEGORIES* printed
    with their markers.

- [variable] *PRINT-PARENT* T

    When an EVENT is signalled and its parent TRIAL's type matches
    *PRINT-PARENT*, the trial is printed as if its TRIAL-START matched
    the PRINT argument of TRY.
    
    ```common-lisp
    (let ((*print* 'leaf)
          (*print-parent* t))
      (with-test (t0)
        (is t)
        (is t)))
    .. T0
    ..   ⋅ (IS T)
    ..   ⋅ (IS T)
    .. ⋅ T0 ⋅2
    ..
    ==> #<TRIAL (WITH-TEST (T0)) EXPECTED-SUCCESS 0.000s ⋅2>
    ```
    
    ```common-lisp
    (let ((*print* 'leaf)
          (*print-parent* nil))
      (with-test (t0)
        (is t)
        (is t)))
    .. ⋅ (IS T)
    .. ⋅ (IS T)
    ..
    ==> #<TRIAL (WITH-TEST (T0)) EXPECTED-SUCCESS 0.000s ⋅2>
    ```
    
    *PRINT-PARENT* NIL combined with printing VERDICTs results in a flat
     output:
    
    ```common-lisp
    (let ((*print* '(or leaf verdict))
          (*print-parent* nil))
      (with-test (outer)
        (with-test (inner)
          (is t :msg "inner-t"))
        (is t :msg "outer-t")))
    .. ⋅ inner-t
    .. ⋅ INNER ⋅1
    .. ⋅ outer-t
    .. ⋅ OUTER ⋅2
    ..
    ==> #<TRIAL (WITH-TEST (OUTER)) EXPECTED-SUCCESS 0.000s ⋅2>
    ```


- [variable] *PRINT-INDENTATION* 2

    The number of spaces each printed TRIAL increases the indentation
    of its children.

- [variable] *PRINT-DURATION* NIL

    If true, the number of seconds spent during execution is printed.
    
    ```common-lisp
    (let ((*print-duration* t)
          (*debug* nil)
          (*describe* nil))
      (with-test (timed)
        (is (progn (sleep 0.3) t))
        (is (progn (sleep 0.2) t))
        (error "xxx")))
    ..        TIMED
    ..  0.300   ⋅ (IS (PROGN (SLEEP 0.3) T))
    ..  0.200   ⋅ (IS (PROGN (SLEEP 0.2) T))
    ..          ⊟ ""xxx (SIMPLE-ERROR)
    ..  0.504 ⊟ TIMED ⊟1 ⋅2
    ..
    ==> #<TRIAL (WITH-TEST (TIMED)) ABORT* 0.504s ⊟1 ⋅2>
    ```
    
    Timing is available for all OUTCOMEs (i.e. for @TRY/CHECKS and
    TRIALs). Checks generally measure the time spent during evaluation
    the form they are wrapping. Trials measure the time between
    TRIAL-START and the VERDICT.
    
    Timing information is not available for TRIAL-START and ERROR\*
    events.

- [variable] *PRINT-COMPACTLY* NIL

    EVENTs whose type matches *PRINT-COMPACTLY* are printed less
    verbosely. LEAF events are printed only with their marker, and
    VERDICTs of trials without printed child trials are printed with `=>
    <MARKER>` (see *CATEGORIES*).
    
    ```common-lisp
    (let ((*print-compactly* t)
          (*debug* nil)
          (*describe* nil))
      (with-test (outer)
        (loop repeat 10 do (is t))
        (with-test (inner)
          (is t)
          (is nil)
          (error "xxx"))
        (loop repeat 10 do (is t))))
    .. OUTER ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅
    ..   INNER ⋅⊠⊟ => ⊟
    ..   ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅
    .. ⊠ OUTER ⊟1 ⊠1 ⋅21
    ..
    ==> #<TRIAL (WITH-TEST (OUTER)) UNEXPECTED-FAILURE 0.000s ⊟1 ⊠1 ⋅21>
    ```
    
    *PRINT-COMPACTLY* has no effect on events being `DESCRIBE`d.

- [variable] *DEFER-DESCRIBE* NIL

    When an EVENT is to be `*DESCRIBE*`d and its type matches
    *DEFER-DESCRIBE*, then instead of printing the often longish context
    information in the tree of events, it is deferred until after TRY
    has finished. The following example only prints LEAF events (due to
    *PRINT* and *PRINT-PARENT*) and in compact form (see
    *PRINT-COMPACTLY*), deferring description of events matching
    *DESCRIBE* until the end.
    
    ```common-lisp
    (let ((*print* 'leaf)
          (*print-parent* nil)
          (*print-compactly* t)
          (*defer-describe* t)
          (*debug* nil))
      (with-test (outer)
        (loop repeat 10 do (is t))
        (with-test (inner)
          (is (= (1+ 5) 7)))))
    .. ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⊠
    ..
    .. ;; UNEXPECTED-RESULT-FAILURE (⊠) in OUTER INNER:
    .. (IS (= #1=(1+ 5) 7))
    .. where
    ..   #1# = 6
    ..
    ==> #<TRIAL (WITH-TEST (OUTER)) UNEXPECTED-FAILURE 0.000s ⊠1 ⋅10>
    ```


### Counting Events

TRIALs have a counter for each category in *CATEGORIES*. When an
EVENT is recorded by TRY and its type matches *COUNT*, the counters
of all categories matching the event type are incremented in the
CURRENT-TRIAL. When a trial finishes and a VERDICT is recorded, the
trial's event counters are added to that of its parent's (if any).
The counts are printed with VERDICTs (see @TRY/PRINT).

If both *COUNT* and *CATEGORIES* are unchanged from the their
default values, then only LEAF events are counted, and we get
separate counters for ABORT\*, UNEXPECTED-FAILURE,
UNEXPECTED-SUCCESS, SKIP, EXPECTED-FAILURE, and EXPECTED-SUCCESS.

```common-lisp
(let ((*debug* nil))
  (with-test (outer)
    (with-test (inner)
      (is t))
    (is t)
    (is nil)))
.. OUTER
..   INNER
..     ⋅ (IS T)
..   ⋅ INNER ⋅1
..   ⋅ (IS T)
..   ⊠ (IS NIL)
.. ⊠ OUTER ⊠1 ⋅2
..
==> #<TRIAL (WITH-TEST (OUTER)) UNEXPECTED-FAILURE 0.000s ⊠1 ⋅2>
```

As the above example shows, EXPECTED-VERDICT-SUCCESS and
EXPECTED-RESULT-SUCCESS are both marked with `"⋅"`, but only
EXPECTED-RESULT-SUCCESS is counted due to *COUNT* being LEAF.

### Collecting Events

When an EVENT is recorded and the type of the EVENT matches the
COLLECT type argument of TRY, then a corresponding object is pushed
onto CHILDREN of the CURRENT-TRIAL for subsequent @TRY/RERUN or
@TRY/REPLAY.

In particular, if the matching event is a LEAF, then the event
itself is collected. If the matching event is a TRIAL-EVENT, then
its TRIAL is collected. Furthermore, trials
which collected anything are always collected by their parent.

By default, both implicit and explicit calls to TRY collect the
UNEXPECTED (see *COLLECT* and *TRY-COLLECT*), and consequently all
the enclosing trials.

- [reader] CHILDREN TRIAL (:CHILDREN = NIL)

    A list of immediate child VERDICTs, RESULTs, and
    ERROR\*s collected in reverse chronological order (see
    @TRY/COLLECT). The VERDICT of this TRIAL is not among CHILDREN,
    but the VERDICTs of child trials' are.

### Rerunning Trials

When a TRIAL is `FUNCALL`ed or passed to TRY, the *test that
created the trial* is invoked, and it may be run again in its
entirety or in part. As the test runs, it may invoke other tests.
Any test (including the top-level one) is skipped if it does not
correspond to a collected trial or its TRIAL-START
event and VERDICT do not match the RERUN argument of TRY. When that
happens, the corresponding function call immediately returns the
TRIAL object.

- A new trial is skipped (as if with SKIP-TRIAL) if RERUN is not T
  and

    - there is no trial representing the same function call among
      the collected but not yet rerun trials in the trial being
      rerun, or

    - the first such trial does not match the RERUN type argument of
      TRY in that neither its TRIAL-START, VERDICT events match the
      type RERUN, nor do any of its collected RESULTs and trials.

- The *test that created the trial* is determined as follows.

    - If the trial was created by calling a DEFTEST function, then
      the test currently associated with that symbol naming the
      function is called with the arguments of the original function
      call. If the symbol is no longer FBOUNDP (because it was
      FMAKUNBOUND) or it no longer names a DEFTEST (it was redefined
      with DEFUN), then an error is signalled.

    - If the trial was created by entering a WITH-TEST form, then
      its body is executed again in the original lexical but the
      current dynamic environment. Implementationally speaking,
      WITH-TEST defines a local function of no arguments (likely a
      closure) that wraps its body, stores the closure in the trial
      object and calls it on a rerun in a WITH-TEST of the same
      TRIAL-VAR and same NAME.

    - If the trial was created by TRY itself to ensure that all
      events are signalled in a trial (see @TRY/EXPLICIT-TRY), then
      on a rerun the same TESTABLE is run again.

    All three possibilities involve entering DEFTEST or WITH-TEST, or
    invoking TRY: the same cases that we have when calling tests
    functions (see @TRY/IMPLICIT-TRY). Thus, even if a trial is rerun
    with FUNCALL, execution is guaranteed to happen under TRY.


### Reprocessing Trials

- [function] REPLAY-EVENTS TRIAL &KEY (COLLECT \*TRY-COLLECT\*) (PRINT \*TRY-PRINT\*) (DESCRIBE \*TRY-DESCRIBE\*) (STREAM \*TRY-STREAM\*) (PRINTER \*TRY-PRINTER\*)

    REPLAY-EVENTS reprocesses the events collected (see @TRY/COLLECT)
    in TRIAL. It takes the same arguments as TRY except
    DEBUG, COUNT and RERUN. This is because
    REPLAY-EVENTS does not run any tests. It simply signals the events
    collected in TRIAL again to allow further processing. The values of
    *CATEGORIES* and *COUNT* that were in effect for TRIAL are used, and
    their current values are ignored to be able to keep consistent
    counts (see @TRY/COUNT).
    
    Suppose we have run a large test using the default `:PRINT 'LEAF`
    `:COLLECT 'UNEXPECTED` arguments for TRY, and now we have too much
    output to look at. Instead of searching for the interesting bits in
    the output, we can replay the events and print only the UNEXPECTED
    events:
    
    ```
    (replay-events ! :print 'unexpected)
    ```
    
    Or we could tell the printer to just print markers for *CATEGORIES*
    and :DESCRIBE at the end:
    
    ```
    (let ((*print-parent* nil)
          (*print-compactly* t)
          (*defer-describe* t)
          (*categories* (ascii-std-categories)))
      (replay-events !))
    .. ................F................!.....
    .. 
    .. ;; UNEXPECTED-FAILURE (F) in SOME-TEST INNER-TEST:
    .. (IS (= 5 6))
    .. debug info
    .. 
    .. ;; UNHANDLED-ERROR (!) in SOME-TEST:
    .. "my-msg" (MY-ERR)
    ```


## Implementation Notes

Try is supported on ABCL, AllegroCL, CLISP, CCL, CMUCL, ECL and
SBCL.

- Pretty printing is non-existent on CLISP and broken on ABCL. The
  output may look garbled on them.

- Gray streams are broken on ABCL so the output may look even worse
  [https://abcl.org/trac/ticket/373](https://abcl.org/trac/ticket/373).

- ABCL, CMUCL, and ECL have a bug related to losing
  EQLness of source literals
  [https://gitlab.com/embeddable-common-lisp/ecl/-/issues/665](https://gitlab.com/embeddable-common-lisp/ecl/-/issues/665).
  The result is somewhat cosmetic, it may cause multiple captures
  being made for the same thing.


## Glossary

- [glossary-term] funcallable instance

    This is a term from the MOP. A funcallable instance is an instance
    of a class that's a subclass of `MOP:FUNCALLABLE-STANDARD-CLASS`. It
    is like a normal instance, but it can also be `FUNCALL`ed.

- [glossary-term] cancelled non-local exit

    This is a term from the Common Lisp ANSI standard. If during the
    unwinding of the stack initiated by a non-local exit another
    nlx is initiated in, and exits from an UNWIND-PROTECT cleanup form,
    then this second nlx is said to have cancelled the first, and the
    first nlx will not continue.
    
    ```common-lisp
    (catch 'foo
      (catch 'bar
        (unwind-protect
             (throw 'foo 'foo)
          (throw 'bar 'bar))))
    => BAR
    ```


* * *
###### \[generated by [MGL-PAX](https://github.com/melisgl/mgl-pax)\]
