TIL - Jest by default calls through

19 Nov 2022

Today I learnt that jest by default calls through to the mocked method.

const item = jest.Mocked<ISomething> = {
    method1: jest.fn(),
    method2: jest.fn()
}

Meaning from the above code that method1 will still call the underlying method’s code. To ensure this does not happen you have to call mockImplementation()

eg.

const item = jest.Mocked<ISomething> = {
    method1: jest.fn().mockImplementation(() => {
        // Do something or do nothing as you wish here.
    }),
    method2: jest.fn()
}

Learning by breaking and failing

TIL - Jest by default calls through