Testing an Array of Objects - Jest

Question

I want to test an array of object. Basically, when I run the test coverage for the shown array of objects, the last object is link have conditions and that's the part which is uncovered.

export const relatedServicesList: IRelatedServiceItem[] = [
  {
    label: 'inquiry.title',
    link: '/adc/declaration/landing',
  },
  {
    label: 'extendDeposit.title',
    link: '/adc/extend-deposit/landing',
  },
  {
    label: 'generalAdminCustomsServices.landing.title',
    link:
      window.location.host === 'stage'
        ? '/demo'
        : '/test',
  },
];

What I tried

import { relatedServicesList } from './routes';
describe('Routes', () => {
  it('when host = stage', () => {
    global.window = Object.create(window);

    Object.defineProperty(window, 'location', {
      value: {
        host: 'stage',
      },
    });
    window.location.host = 'stage';
    expect(relatedServicesList[relatedServicesList.length - 1]).toEqual(
      expect.objectContaining({
        label: 'generalAdminCustomsServices.landing.title',
        link:
          'stage',
      }),
    );
  });

  it('when host != stage', () => {
    global.window = Object.create(window);

    Object.defineProperty(window, 'location', {
      value: {
        host: 'demo',
      },
    });
    window.location.host = 'demo';

    expect(relatedServicesList[relatedServicesList.length - 1]).toEqual(
      expect.objectContaining({
        label: 'generalAdminCustomsServices.landing.title',
        link: '/test',
      }),
    );
  });
});

The condition part is uncovered. Please note that only the array is exported which is of type IRelatedServiceItem there's no function etc.

Lin Du · Accepted Answer · 2020-01-13 03:37:53Z

1

There are two caveats:

If you use es6 import syntax to import relatedServicesList array, the evaluation(window.location.host === 'stage' ? '/demo' : '/test') is before you change the value of window.location. We can use require handle this.
You need to use jest.resetModules() to reset the module registry - the cache of all required modules. So that there will be a new evaluation for each test case.

Here is the working example: index.ts:

interface IRelatedServiceItem {
  label: string;
  link: string;
}

console.log('window.location.host: ', window.location.host);
export const relatedServicesList: IRelatedServiceItem[] = [
  {
    label: 'inquiry.title',
    link: '/adc/declaration/landing',
  },
  {
    label: 'extendDeposit.title',
    link: '/adc/extend-deposit/landing',
  },
  {
    label: 'generalAdminCustomsServices.landing.title',
    link: window.location.host === 'stage' ? '/demo' : '/test',
  },
];

index.spec.ts:

describe('59698218', () => {
  beforeEach(() => {
    jest.resetModules();
  });

  it('when host = stage', () => {
    Object.defineProperty(window, 'location', {
      value: { host: 'stage' },
      writable: true,
    });
    const { relatedServicesList } = require('./index');
    expect(relatedServicesList[relatedServicesList.length - 1]).toEqual({
      label: 'generalAdminCustomsServices.landing.title',
      link: '/demo',
    });
  });

  it('when host != stage', () => {
    Object.defineProperty(window, 'location', {
      value: { host: 'demo' },
      writable: true,
    });
    const { relatedServicesList } = require('./index');
    expect(relatedServicesList[relatedServicesList.length - 1]).toEqual({
      label: 'generalAdminCustomsServices.landing.title',
      link: '/test',
    });
  });
});

Unit test results with 100% coverage:

 PASS  src/stackoverflow/59698218/index.spec.ts (8.497s)
  59698218
    ✓ when host = stage (14ms)
    ✓ when host != stage (2ms)

  console.log src/stackoverflow/59698218/index.ts:107
    window.location.host:  stage

  console.log src/stackoverflow/59698218/index.ts:107
    window.location.host:  demo

----------|----------|----------|----------|----------|-------------------|
File      |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
----------|----------|----------|----------|----------|-------------------|
All files |      100 |      100 |      100 |      100 |                   |
 index.ts |      100 |      100 |      100 |      100 |                   |
----------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        9.649s

Source code: https://github.com/mrdulin/jest-codelab/tree/master/src/stackoverflow/59698218

answered Jan 13, 2020 at 3:37

Lin Du

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4 Comments

Nadeem Ahmad Over a year ago

Thank you for your answer, the last answer that you have provided help me well as well, but there is an issue that's; It's covering the if part but not the else part. Can you help me with that ? Answer Link : stackoverflow.com/questions/59627009/…

Lin Du Over a year ago

@NadeemAhmad OK. I will update the answer, make it 100% coverage

Lin Du Over a year ago

@NadeemAhmad Sure. But I will reply to you after I finish my work.

Nadeem Ahmad Over a year ago

No problem at all, can you paste your email or hit me on [email protected] ?

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