jest mock call

1describe("mockImplementation", () => {
2  test("function", () => {
3    const mockFn1 = jest.fn().mockImplementation(() => 42);
4    const mockFn2 = jest.fn(() => 42);
5
6    expect(mockFn1()).toBe(42);
7    expect(mockFn2()).toBe(42);
8  });

1test("es6 class", () => {
2    const SomeClass = jest.fn();
3    const mMock = jest.fn();
4
5    SomeClass.mockImplementation(() => {
6      return {
7        m: mMock
8      };
9    });
10
11    const some = new SomeClass();
12    some.m("a", "b");
13    expect(mMock.mock.calls).toEqual([["a", "b"]]);
14  });

1test("mock.calls", () => {
2  const mockFn = jest.fn();
3  mockFn(1, 2);
4
5  expect(mockFn.mock.calls).toEqual([[1, 2]]);
6});

1test("mock.instances", () => {
2  const mockFn = jest.fn();
3
4  const a = new mockFn();
5  const b = new mockFn();
6
7  mockFn.mock.instances[0] === a;
8  mockFn.mock.instances[1] === b;
9});