Avoid the need to cast mocked typescript imports

Question

I'm importing a mocked function, but since Typescript doesn't seem to know that Jest changes the import to a mock, I have to cast the imported function before I can use mock methods like mockReturnValue etc.

jest.mock('../myImport');
import { thisFunctionIsMocked } from '../myImport'

/* ... */

(<Mock<any>>thisFunctionIsMocked).mockReturnValue(42);

If I don't cast the import, Typescript claims that the mock function methods don't exist. Is there a better way to do this?

Answer 1

I've been looking for the same. Unfortunately, doesn't seem to be much out there on how to handle this. Some alternatives, however.

1) Slightly different syntax for what you're already doing:

(thisFunctionIsMocked as jest.Mock).mockReturnValue(42);

2) Use require and cast there instead:

const thisFunctionIsMocked = require('../myImport') as jest.Mock;

Update:

ts-jest now has a mocked helper which you can use. You still need to use it when you reference mocked imports, but it means that the type signature of the original source isn't lost:

import { mocked } from 'ts-jest/utils';

test('direct', () => {
  foo.name();
  expect(mocked(foo.name).mock.calls).toHaveLength(1);
});