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

There are two solutions, both are casting desired function

1) Use jest.MockedFunction

import * as dep from './dependency';

jest.mock('./dependency');

const mockMyFunction = dep.myFunction as jest.MockedFunction;

2) Use jest.Mock

import * as dep from './dependency';

jest.mock('./dependency');

const mockMyFunction = dep.default as jest.Mock;

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There is no difference between these two solutions. The second one is shorter and I would therefore suggest using that one.

Both casting solutions allows to call any jest mock function on mockMyFunction like mockReturnValue or mockResolvedValue https://jestjs.io/docs/en/mock-function-api.html

mockMyFunction.mockReturnValue('value');

mockMyFunction can be used normally for expect

expect(mockMyFunction).toHaveBeenCalledTimes(1);