Solving the Mysterious Case of the Empty Angular Unit Test Coverage Report HTML

Have you ever spent hours writing unit tests for your Angular application, only to be met with a frustratingly empty HTML report? You’re not alone! In this article, we’ll dive into the possible causes of this phenomenon and provide a step-by-step guide to resolving the issue and generating a comprehensive test coverage report.

Why is my Angular unit test coverage report HTML empty?

Before we dive into the solutions, let’s explore some common reasons why your Angular unit test coverage report HTML might be empty:

• Incorrect configuration: Misconfigured Jest or Istanbul settings can lead to an empty report.
• Missing dependencies: Failing to install or import required dependencies, such as @angular-devkit/build-angular, can cause issues.

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• Invalid test syntax: Incorrectly written or structured tests can prevent the report from generating.
• Code coverage threshold: If the code coverage threshold is set too high, the report might not generate.

Step 1: Verify your project configuration

Let’s start by ensuring your project configuration is correct:

1. Open your angular.json file and verify that the test section is present and correctly configured:

{
  "$schema": "./node_modules/@angular-devkit/core/src/workspace/schema.json",
  "version": 2,
  "projects": {
    "my-app": {
      ...
      "architect": {
        "test": {
          "builder": "@angular-devkit/build-angular:karma",
          "options": {
            "main": "src/test.ts",
            "polyfills": "src/polyfills.ts",
            "tsConfig": "src/tsconfig.spec.json",
            "karmaConfig": "src/karma.conf.js"
          }
        }
      }
    }
  }
}

Step 2: Install and import required dependencies

Next, ensure you’ve installed and imported the necessary dependencies:

1. Run the following command in your terminal to install the required dependencies:

npm install --save-dev @angular-devkit/build-angular @types/jest

Step 3: Write valid unit tests

Now, let’s focus on writing valid unit tests using Jest and Angular’s testing framework:

1. Create a new test file, e.g., my.component.spec.ts, and write a simple test:

import { TestBed, async } from '@angular/core/testing';
import { MyComponent } from './my.component';

describe('MyComponent', () => {
  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [ MyComponent ]
    }).compileComponents();
  }));

  it('should create the component', async(() => {
    const fixture = TestBed.createComponent(MyComponent);
    const component = fixture.componentInstance;
    expect(component).toBeTruthy();
  }));
});

Step 4: Configure Istanbul for code coverage

To generate a comprehensive code coverage report, we need to configure Istanbul:

1. Create a new file, karma.conf.js, and add the following configuration:

module.exports = function (config) {
  config.set({
    ...
    coverageReporter: {
      dir: require('path').join(__dirname, './coverage/my-app'),
      subdir: '.',
      type: 'html'
    }
  });
};

Step 5: Run your unit tests with code coverage

Now, let’s run our unit tests with code coverage enabled:

1. Run the following command in your terminal:

ng test --code-coverage

Step 6: Verify your report

After running the tests, navigate to the coverage/my-app directory and open the generated HTML report:

You should now see a comprehensive report detailing the code coverage of your Angular application.

File	Stmts	Branch	Funcs	Lines	Uncovered Line %
src/app/my.component.ts	20	10	5	15	20%
src/app/my.service.ts	30	15	10	20	30%

Common issues and solutions

If you’re still encountering issues, here are some common problems and their solutions:

• Error: Cannot find module ‘jest’ or ‘@angular-devkit/build-angular’: Ensure you’ve installed the required dependencies and imported them correctly in your test files.
• Error: HTML report not generated: Verify that your Istanbul configuration is correct, and the report directory is correctly specified.
• Test files not being executed: Check that your test files are being properly loaded and executed by Jest.

Conclusion

Remember to regularly review and improve your test coverage to ensure the quality and reliability of your Angular application.

Frequently Asked Questions

Stuck with an empty Angular unit test coverage report? Don’t worry, we’ve got you covered!

Why is my Angular unit test coverage report HTML file empty?

This might be due to a misconfiguration in your Karma or Jasmine setup. Check that you’ve correctly set up your test coverage reporter, and that your tests are actually running. Also, make sure you’ve installed the required dependencies, such as `karma-coverage` or `jasmine-reporters`.

How do I configure Karma to generate a test coverage report?

You’ll need to add the `coverageReporter` to your Karma configuration file (usually `karma.conf.js`). Set the `type` property to `html` and specify the `dir` where you want the report to be generated. For example: `coverageReporter: { type: 'html', dir: 'coverage/' },

What is the minimum required setup for generating a test coverage report in Angular?

You’ll need to install `@angular-devkit/build-angular` and `karma-coverage` (or `jasmine-reporters` for Jasmine). Then, update your `angular.json` file to include the `test` and `coverage` configurations. Finally, run `ng test –code-coverage` to generate the report.

Why is my Angular test coverage report showing 0% coverage?

This might be because you haven’t actually written any tests for your components or services. Make sure you’ve created test files (e.g., `component.spec.ts`) and written valid tests using Jasmine or Mocha. Also, check that your tests are running successfully and that you’ve correctly instrumented your code for coverage analysis.

Can I customize the appearance of my Angular test coverage report?

Yes, you can customize the report by using a custom reporter or template. For example, you can use `karma-coverage-istanbul-reporter` to generate reports in different formats, such as HTML, LCOV, or Cobertura. You can also create a custom reporter using the Istanbul API.

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