Mock dependency in jest with typescript

Question

When testing a module that has a dependency in a different file. When assigning that module to be jest.Mock typescript gives an error that the method mock

Answer 1

Use as jest.Mock and nothing else

The most concise way of mocking a module exported as default in ts-jest that I can think of really boils down to casting the module as jest.Mock.

Code:

import myDep from '../dependency' // No `* as` here

jest.mock('../dependency')

it('does what I need', () => {
  // Only diff with pure JavaScript is the presence of `as jest.Mock`
  (myDep as jest.Mock).mockReturnValueOnce('return')

  // Call function that calls the mocked module here

  // Notice there's no reference to `.default` below
  expect(myDep).toHaveBeenCalled()
})

Benefits:

• does not require referring to the default property anywhere in the test code - you reference the actual exported function name instead,
• you can use the same technique for mocking named exports,
• no * as in the import statement,
• no complex casting using the typeof keyword,
• no extra dependencies like mocked.