jest.mock factory doesn't work inside a test

[tleunen]

Do you want to request a feature or report a bug?
Bug

What is the current behavior?

It seems the way to create a mock with a factory doesn't work inside test or it. It works only when the mock is defined at the root level of the file.

Here's my example of a mock:

jest.mock('services/feature', () => ({
    isEnabled: () => true
}));

What is the expected behavior?

Mocking a file inside a test should work.

Please provide your exact Jest configuration and mention your Jest, node, yarn/npm version and operating system.

Jest 18.0.0, Node 7.4, macOS

[thymikee]

jest.mock calls are automatically hoisted to the top of the file with babel-jest transform. You can omit this behaviour with jest.doMock. Have you tried that?

[tleunen]

Same thing with doMock.

In the docs, I can read

Note: When using babel-jest, calls to mock will automatically be hoisted to the top of the code block. Use doMock if you want to explicitly avoid this behavior.

But... A test is a code block, right? So in my case, I don't expect to see any differences.

Here's a full test

it('renders with the enabled feature', () => {
  jest.mock('services/feature', () => ({
      isEnabled: () => true
  }));

  const component = renderer.create(
      <MyComponent />
  );

  const tree = component.toJSON();
  expect(tree).toMatchSnapshot();
});

[thymikee]

Could you provide a repro of this in a GH repository?

[tleunen]

Sure. Here it is: https://github.com/tleunen/jest-issue-2582

Both tests render "Disabled" even though one of then has a mock to renders "Enabled" instead.
See these:
https://github.com/tleunen/jest-issue-2582/blob/master/src/MyComponent.js
https://github.com/tleunen/jest-issue-2582/blob/master/src/__tests__/MyComponent.spec.js

Thanks.

[tleunen]

Any advice @thymikee @cpojer for this issue?
I have several tests in the same file and I'd like to have different mock responses for each of them.

[publicJorn]

Glad I found this issue, I was breaking my head whyjest.mock() didn't work in my describe scope. Moved it to the top (below my imports in the test file) and it works.

For me it also applies to jest.mock() without a factory, using a __mocks__ folder containing the mocked file.

--edit

It's obviously necessary to hoist the jest.mock() statement to before the import statements. However @tleunen, this probably means it's not possible to mock the same file more then once, with different responses. Maybe you are best served by making the factory function more dynamic, so it can serve you different results in each test case.

In my mind it would make it more explicit if jest.mock() is always put outside the describe and it blocks. But this should then be clearly stated in the docs

[thymikee]

So jest.mock is being hoisted to the function scope, that's why it won't work with requires (and definitely not imports which are hoisted to module scope) if you call it inside a function other than describe (which is treated specially by Jasmine).
Your jest.mock call will be hoisted to the top of that very function (not the module), that's why it won't work the way you expect.

Generally we advise to setup different mocks in beforeEach and afterEach if you want them different across test cases.

@cpojer could elaborate on this in detail, and if we want to hoist the calls to the upper scopes.

[cpojer]

This is because you are requiring your modules when the module initializes (using import). jest.mock gets called way later. The way to solve this is:

beforeEach(() => { // or the specific test
  jest.mock('MyModule', () => …);
  const MyModule = require('MyModule');
  …
});

etc.

[Psykar]

If you were to do this in beforeEach, I'm unclear how you'd differentiate tests (so how would you be giving a different mock for each test?)

Putting it inside the tests themselves works of course.

[MartinCerny-awin]

Can you then pass mocked module inside the tested component?