Exploring the world of mocking tests using Jest and inputs

Question

Exploring the world of mocking tests using Jest and inputs

Is there a way to create a jest test specifically for this function?

const input = require('prompt-sync')();

export function choices(): void {
    const choice = input("Choose a letter");
    if (choice === "a") {
        console.log("Airplane");
    } if (choice === "b") {
        console.log("Balloon");
    } else {
        console.log("Neither");
    }

}

I am aware that mocking is necessary in this scenario. However, I am uncertain about how to implement it when the input is stored within the function itself rather than being passed as a parameter. I would prefer not to alter this setup.

typescript input jestjs

Answer 1

Answer №1

To mock the prompt-sync module in your tests, you can utilize the jest.mock function. This module returns a function that provides your input, so your Jest.mock setup would look something like this:

const mockInput = jest.fn();
jest.mock("prompt-sync", () => () => mockInput);

Make sure to include this setup before importing the module in your test file.

Here is a complete example:

const mockInput = jest.fn();
jest.mock("prompt-sync", () => () => mockInput);

import { choices } from "../path/to/file";

describe("test", () => {
  let consoleSpy: jest.SpyInstance;

  beforeEach(() => {
    consoleSpy = jest.spyOn(console, "log");
  });

  afterEach(() => {
    jest.resetAllMocks();
  });

  it("should call the input", () => {
    choices();

    expect(mockInput).toHaveBeenCalledWith("Choose a letter");
  });

  it("should call 'A'", () => {
    mockInput.mockReturnValue("a");

    choices();

    expect(consoleSpy).toHaveBeenCalledWith("Airplane");
  });
});

I recommend refactoring your code to improve its testability.

Answer 2

To mock the prompt-sync module in your tests, you can utilize the jest.mock function. This module returns a function that provides your input, so your Jest.mock setup would look something like this:

const mockInput = jest.fn();
jest.mock("prompt-sync", () => () => mockInput);

Make sure to include this setup before importing the module in your test file.

Here is a complete example:

const mockInput = jest.fn();
jest.mock("prompt-sync", () => () => mockInput);

import { choices } from "../path/to/file";

describe("test", () => {
  let consoleSpy: jest.SpyInstance;

  beforeEach(() => {
    consoleSpy = jest.spyOn(console, "log");
  });

  afterEach(() => {
    jest.resetAllMocks();
  });

  it("should call the input", () => {
    choices();

    expect(mockInput).toHaveBeenCalledWith("Choose a letter");
  });

  it("should call 'A'", () => {
    mockInput.mockReturnValue("a");

    choices();

    expect(consoleSpy).toHaveBeenCalledWith("Airplane");
  });
});

I recommend refactoring your code to improve its testability.

Exploring the world of mocking tests using Jest and inputs

Answer №1

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