Question 167647 in Javascript Question posted in
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Javascript – Testing if one method is being called by another using Jest

I am using Jest for my testing environment and I am trying to see if a method in the tested module calls another method at least once.

Here is the nested.js module:

export function getUserData() {
  console.log("CALLING API");
  const user = {
    name: "user",
  };
  setUserData(user);
}

export function setUserData(user) {
  console.log("Setting user data");
}

And here is the nested.test.js:

import * as nested from "../nested";
let storeUserDataSpy = jest.spyOn(nested, "setUserData");

describe("Get user data calls child method", () => {
  it("should call the child method", async () => {
    nested.getUserData();
    expect(storeUserDataSpy).toHaveBeenCalledTimes(1);
  });
});

The error that I am getting is that the method has not been called at all:

    Expected number of calls: 1
    Received number of calls: 0

I tried various ways of resolving the issue including jest.mock and including the actual methods from the nested.js module.

What I don’t want to do is to spyOn console logs as these won’t be included in the production code.

I uploaded the code with all the Jest and Babel config to a GitHub repo.

Here are the steps to try it locally:

git clone [email protected]:verebes1/tests-jest.git
cd tests-jest
npm install
npm run test
Tags:

2

Answers


  1. Chosen as BEST ANSWER
    0

    I found a solution based on another answer by using the Rewire package, and by including it as a babel plugin. Here is the code:

    nested.js

    export function getUserData() {
  console.log("CALLING API");
  const user = {
    name: "user",
  };
  setUserData(user);
}

export function setUserData(user) {
  console.log("Setting user data");
}

    And the nested.test.js

    import __RewireAPI__, * as nested from "../nested";
let storeUserDataSpy = jest.spyOn(nested, "setUserData");

describe("Get user data calls child method", () => {
  it("should call the child method", async () => {
    __RewireAPI__.__Rewire__('setUserData', storeUserDataSpy);
    nested.getUserData();
    expect(storeUserDataSpy).toHaveBeenCalledTimes(1);
  });
});

    finally .babelrc

    {
  "presets": [
    "@babel/preset-env"
  ],
  "plugins": [
    "rewire"
  ]
}

    The answer-from-stack-overflow-using-rewire branch on the repo is updated with the above


  2. 0

    Easy way to achieve that is to extract function you want to spy on to separate file and spy on that.

    Test file nested.test.js

    import {getUserData} from "../nested";
import * as utils from './utils'


let storeUserDataSpy = jest.spyOn(utils, "setUserData");

describe("Get user data calls child method", () => {
  it("should call the child method", async () => {
    getUserData();
    expect(storeUserDataSpy).toHaveBeenCalledTimes(1);
  });
});

    Code file nested.js

    import {setUserData} from "./test/utils";

export function getUserData() {
  console.log("CALLING API");
  const user = {
    name: "user",
  };
  setUserData(user);
}

    Utils utils.js

    export function setUserData(user) {
    console.log("Setting user data");
}
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