Today I realized we had an issue in a test (Jest)
We have a function that emits CustomEvents
In our Jest test, we define a listener and check that it's called with the expected event
I tried changing the detail (the internal object) of the custom event
... and the test was still passing 🤔
test('events.voiceEvent() emits "CustomEvent{ lavoiceevent }" event', () => { const expectedEvent = new CustomEvent('lavoiceevent', { detail: { event: 'USER_SAID_HELLO_ERRRRROR' }, }); window.addEventListener('lavoiceevent', listener); events.voiceEvent('USER_SAID_HELLO'); expect(listener).toHaveBeenCalledWith(expectedEvent); // ✅ expect(listener).toHaveBeenCalledTimes(1); }); The problem is this line won't work as expected (its an issue related with the serialization of the Events)
expect(listener).toHaveBeenCalledWith(expectedEvent) In order to solve this (and make our test does check the detail of the event) we should use "mock.calls" as:
test('events.voiceEvent() emits "CustomEvent{ lavoiceevent }" event', () => { const listener = jest.fn(); window.addEventListener('lavoiceevent', listener); events.voiceEvent('USER_SAID_HELLO'); expect(listener).toHaveBeenCalledTimes(1); expect(listener).toHaveBeenCalledWith(expect.any(CustomEvent)); const ev = listener.mock.calls[0][0]; expect(ev.type).toBe('lavoiceevent'); expect(ev.detail.event).toBe('USER_SAID_HELLO'); // 🔥 will fail otherwise }); --
thanks for reading.
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