Methods

The verifier for functions: should().method(fn) checks that invoking the function throws — or that it completes and hands the produced value back for further chains.

`should().method(fn).throws(...)`

should().method(() => service.cancel(id)).throws();
should().method(() => service.get(id)).not.throws();

throws(...args) invokes the function with the given arguments and passes when the call throws any exception. not.throws() is the readable replacement for a hand-rolled "called and nothing exploded" try/catch.

`returns(...args)` — run and keep the value

returns(...args) invokes the function, asserts that it completes without throwing, and returns the produced value — the bridge from a method check back to the typed verifiers:

const age = should().method(() => user.age).returns();
should().number(age).positive();

Under not, returns() asserts the opposite — the invocation must throw — and yields undefined.

Definedness

Like every verifier, should().method(null).throws() throws The entry is not defined. regardless of not; use defined()/not.defined() when the function itself may be absent — a not-yet-assigned callback, an optional dependency.

When to use what

Situation	Use
The call must fail	`method(fn).throws()`
The call must succeed and the value matters	`method(fn).returns()` + a typed verifier
The call must succeed and the value does not matter	`method(fn).not.throws()`

Signatures and messages

See API reference — Method verifier.

16 September 2026