    GET http://localhost:8000/predicates-string

    HTTP 200
    [Asserts]
    body == "Hello World!"
    body startsWith "Hello"
    body endsWith "!"
    body contains "llo"
    body matches "Hello [a-zA-Z]+!"
    body matches /Hello [a-zA-Z]+!/

    GET http://localhost:8000/predicates-string-empty
    HTTP 200
    [Asserts]
    body == ""
    body exists

    GET http://localhost:8000/predicates-string-unicode
    HTTP 200
    [Asserts]
    body == "\u{2708}"
    bytes count == 3