std::testing

std::testing provides lazy assertion operators and the assertion effect used by yulang test. The prelude re-exports both operators.

The module introduces no data type. Test discovery belongs to the surrounding test facility; see Modules for that mechanism.

Lazy assertion operators

assert condition requires a Boolean result. expected assert_eq actual requires both operands to have the same inferred type.

mod test assertions:
    my truth = assert (2 + 2 == 4)
    my equality = (2 + 2) assert_eq 4

Running this file with yulang test --show-passes reports two passing tests. The left operand of assert_eq is the expected value, and the right operand is the actual value.

Both operators are lazy. assert condition packages the condition as a thunk, while assert_eq packages each operand as a separate thunk. The test runner evaluates those thunks while handling the assertion effect.

Assertion effect

The operator expansions call the two operations of the assertion effect:

Operation	Signature
assertion::assert check	(() -> [_] bool) -> [assertion] ()
assertion::assert_eq (expected, actual)	(() -> [_] 'a, () -> [_] 'a) -> [assertion] ()

The operations can also be called directly by passing thunks:

mod test direct_operations:
    my truth = assertion::assert (\() -> true)
    my equality =
        assertion::assert_eq ((\() -> 4), (\() -> 4))

The built-in test runner handles assertion. Code that runs these operations under another entry point needs a matching handler.

Failure reporting

assert fails the current test when its thunk returns false. assert_eq fails when its two thunks return unequal values. The test runner points to the operator and, for assert_eq, labels the left value as expected and the right value as actual.

The current assert_eq signature has no Eq, Display, or Debug prerequisite. Its operands must still have the same inferred type.

Quick reference

Surface	Result
assert condition	Lazily emit assertion for a bool expression
expected assert_eq actual	Lazily emit assertion for two values of the same type
assertion::assert check	Run a Boolean thunk through [assertion]
assertion::assert_eq (expected, actual)	Run two same-typed thunks through [assertion]

See also

• Modules → Test modules — test discovery and execution
• Effects — effect declarations, operations, and handlers
• Standard Library Catalogue — the full module inventory