Asserting on Mocks in Vitest
From the Vitest cheat sheet · Mock Functions · verified Nov 2026
Asserting on Mocks
Check how a mock was called, what it returned, and in which order
typescript
expect(fn).toHaveBeenCalled()
expect(fn).toHaveBeenCalledTimes(2)
expect(fn).toHaveBeenCalledWith('ada', { admin: true })
expect(fn).toHaveBeenLastCalledWith('grace')
expect(fn).toHaveBeenCalledExactlyOnceWith('ada')
expect(fn).toHaveReturnedWith(42)📌 Pass the mock itself, not a call: expect(fn), not expect(fn())
💡 toHaveBeenCalledExactlyOnceWith checks count and args together
🔍 mock.calls is an array of argument arrays, one per call
⚡ Mix in matchers: toHaveBeenCalledWith(expect.any(String))
toHaveBeenCalledWithmock.callsspy-assertions
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