JAVASCRIPT

jest mock method by name

import Foo from './Foo';
import Bar from './Bar';

jest.mock('./Bar');

describe('Foo', () => {
  it('should return correct foo', () => {
    // As Bar is already mocked,
    // we just need to cast it to jest.Mock (for TypeScript) and mock whatever you want
    (Bar.prototype.runBar as jest.Mock).mockReturnValue('Mocked bar');
    const foo = new Foo();
    expect(foo.runFoo()).toBe('real foo : Mocked bar');
  });
});

jest mock mockname

test("mockName", () => {
  const mockFn = jest.fn().mockName("mockedFunction");
  mockFn(); // comment me
  expect(mockFn).toHaveBeenCalled();
});

jest mock call

test("mock.calls", () => {
  const mockFn = jest.fn();
  mockFn(1, 2);

  expect(mockFn.mock.calls).toEqual([[1, 2]]);
});