jest mock simple js function code example

Example 1: jest mock implementation

describe("mockImplementation", () => {
  test("function", () => {
    const mockFn1 = jest.fn().mockImplementation(() => 42);
    const mockFn2 = jest.fn(() => 42);

    expect(mockFn1()).toBe(42);
    expect(mockFn2()).toBe(42);
  });

Example 2: jest mock call

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

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