jest mock object method 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 class
test("es6 class", () => {
const SomeClass = jest.fn();
const mMock = jest.fn();
SomeClass.mockImplementation(() => {
return {
m: mMock
};
});
const some = new SomeClass();
some.m("a", "b");
expect(mMock.mock.calls).toEqual([["a", "b"]]);
});
Example 3: jest mock call
test("mock.calls", () => {
const mockFn = jest.fn();
mockFn(1, 2);
expect(mockFn.mock.calls).toEqual([[1, 2]]);
});
Example 4: jest mock instance
test("mock.instances", () => {
const mockFn = jest.fn();
const a = new mockFn();
const b = new mockFn();
mockFn.mock.instances[0] === a;
mockFn.mock.instances[1] === b;
});