What is the proper way to implement jest.mock in a describe or it block?

Using typescript and jest, I am faced with a scenario involving two files: users.service.ts, which imports producer.ts. In an attempt to mock a function in producer.ts, I successfully implement it.

import { sendUserData } from "./users.service";

const processDataSpy = jest.fn().mockImplementation(() => {
    throw new Error("failed");
});

jest.mock("../users/manager", () => ({
    sendEvent: async (arg1: string, arg2: string, arg3: any) =>
        processDataSpy(arg1, arg2, arg3),
}));


describe("users.service", () => {

    it("invokes endpoint and returns proper data if unsuccessful", async () => {

        const result = await sendUserData(data);

        expect(result).toBe(false);

    });

However, my goal is to simulate different outcomes in processDataSpy. While currently testing for the error-throwing case as shown above, I also wish to test scenarios where no error is thrown. How can I achieve testing multiple cases without compromising the integrity of the test?

it("invokes endpoint and returns proper data if unsuccessful", async () => {
    
    jest.mock("../users/manager", () => ({
        sendEvent: async (arg1: string, arg2: string, arg3: any) =>
            processDataSpy(arg1, arg2, arg3),
    }));
    ...
    const result = await sendUserData(data);

    expect(result).toBe(false);

});

Upon attempting to move the "jest.mock" within the "it" block, I encounter an error suggesting that the mock is either unused or not initialized properly. Is there a way to utilize "jest.mock" within a "describe" or "it" block effectively?

Answer №1

To implement

processDataSpy.mockImplementation
, you can include it within either the it or test block.

// To potentially reset the mock before each test
beforeEach(() => {
  processDataSpy.mockReset(); 
});

it('Exploring another scenario', async () => {
    
    processDataSpy.mockImplementation(() => {
      throw new Error('Different error');
    })
   
    const result = await sendingUserData(
      information
    );

    expect(result).toBe(false);
});

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