jest mock implementationonce code example

Example 1: how to mock a library in jest

import randomColor from "randomcolor";


jest.mock("randomColor", () => {
  return {
    randomColor: () => {
      return mockColor('#123456');
    }
  }
});
let mockColor = jest.fn();

Example 2: 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);
  });