Jest Mock in TypeScript

Writing tests in TypeScript in quite painful, especially when using mock.

ts
import { readFile } from './fs-util';
jest.mock('./fs-util');
(readFile as jest.MockInstance).mockImplementation((path: string) => {
    ...
});

ts
import { readFile } from './fs-util';
jest.mock('./fs-util');
(readFile as jest.MockInstance).mockImplementation((path: string) => {
    ...
});

If you’re using ts-jest (which you probably already are if you write your tests in TypeScript), it provides a mocked helper.

ts
import { mocked } from 'ts-jest/utils';
import { readFile } from './fs-util';
jest.mock('./fs-util');
mocked(readFile).mockImplementation(path => {
    ...
});

ts
import { mocked } from 'ts-jest/utils';
import { readFile } from './fs-util';
jest.mock('./fs-util');
mocked(readFile).mockImplementation(path => {
    ...
});