Saturday, November 23, 2019

Example Jest test with an object instantiation inside method under test, then moved out into a utility class

Below are two examples of code and the corresponding unit tests for them. The first example includes an instantiation of an object inside it, the other breaks the instantiation of the object to a utility module.  Both are doable, but the latter way easier to unit test.

Environment:
CentOS Linux release 7.3.1611 (Core)
node v8.16.0
jest 24.8.0


Instantiating a new object inside method of test:
sampleOld.js
const cherryshoeAuthorization = require("cherry-shoe-auth");

const processValidRequest = async (requestType, jsonRequestData) => {
  const authService = new cherryshoeAuthorization.CherryshoeAuthorization("cherryshoe.com");
  const userData = await authService.getSessionData(jsonRequestData.token);
  const dbResponse = await requestTypeHandlers[requestType](jsonRequestData, userData.username);
};

sampleOld.test.js

const unit = require(./sampleOld);

// import external dependencies for mocking
const cherryshoeAuthorization = require('cherry-shoe-auth');

// mock cherry-shoe-auth
jest.genMockFromModule('cherry-shoe-auth');
jest.mock('cherry-shoe-auth');

test('Test processValidRequests', async () => {

  // mock external dependency method(s)
  const mockCherryshoeAuthorization = {
    getSessionData: jest.fn(),
  }

  cherryshoeAuthorization.CherryshoeAuthorization.mockImplementation(() => mockCherryshoeAuthorization);

  // mock return values that external dependency method(s) will return
  const userData = {
    firstname: "firstname",
    lastname: "lastname",
    username: "username",
  }

  mockCherryshoeAuthorization.getSessionData.mockReturnValue(userData);

  // unit under test
  // function returns nothing so nothing to expect with a return
  await expect(unit.processValidRequest(requestType, jsonRequest)).resolves;

  // verify that mock method(s) were expected to be called
  expect(mockCherryshoeAuthorization.getSessionData).toHaveBeenCalledTimes(1);
});


Break out instantiation of new object in a auth utility module:

sampleNew.js
const authUtils = require(./authUtils);

const processValidRequest = async (requestType, jsonRequestData) => {
  const userData = await authUtils.getSessionData(jsonRequestData.token);
  const dbResponse = await requestTypeHandlers[requestType](jsonRequestData, userData.username);
};

sampleNew.test.js

const unit = require(./sampleNew);

// import external dependencies for mocking
const authUtils = require(./authUtils);

test('Test processValidRequests', async () => {

  const mockLoginUtilsGetSessiondata = authUtils.getSessionData =
    jest.fn().mockName('mockLoginUtilsGetSessiondata');

  // mock return values that external dependency method(s) will return
  const userData = {
    firstname: "firstname",
    lastname: "lastname",
    username: "username",
  }

  mockLoginUtilsGetSessiondata.mockReturnValue(userData);

  // unit under test
  // function returns nothing so nothing to expect with a return
  await expect(unit.processValidRequest(requestType, jsonRequest)).resolves;

  // verify that mock method(s) were expected to be called

  expect(authUtils.getSessionData).toHaveBeenCalledTimes(1);
});

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