CODEWITHSUNDEEP
typescriptunit-testingjestjs
overdub60
overdub60

Reputation: 738

How to mock object in jest

I'm trying to mock a function of an object with Jest and Typescript and it just does not work. Here is a short version of what I have:

// myModule.ts

export const Foo = {
  doSomething: () => {
    // ... does something
    console.log('original implementation');
  }
}

Then in my test:

jest.mock('.myModule.ts', () => {
  return {
    Foo: {
      doSomething: jest.fn().mockImplementation(() => {
        console.log('mock implementation')
      })
    }
  }
})

// .. further down in the test
Foo.doSomething();

Shouldn't the console.log('mock implementation') be called when I call Foo.doSomething()? It doesn't error and it's not calling the original implementation anymore, but it's also not calling my mockImplementation.

Upvotes: 0

Views: 245

Answers (2)

Chris
Chris

Reputation: 7298

After switching to jest 26.6, I found that none of these worked outside of tests (had been doing it directly below my imports, outside of any describe or it call). If I wanted any kind of mock implementation, I had to set it in the test, or in a beforeEach. If anyone can supply a link to the documentation on this, I'd be obliged.

Upvotes: 0

LoremIpsum
LoremIpsum

Reputation: 4428

Try this:

import { Foo } from './foo';

jest
  .spyOn(Foo, 'doSomething')
  .mockImplementation(() => console.log('mock implementation'));

Foo.doSomething();

Upvotes: 1

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