In this article, I'll explain the steps to run unit test cases for a single spec file and help developers complete Angular unit tests fast. There are many approaches to running Angular unit test cases for a single file, but I will explain the simplest one, which won't affect the code coverage for other team members' unit test cases. 

Step 1

Add the Spec name in the test.ts file under the src folder. 

import 'zone.js/dist/zone-testing';
import { getTestBed } from '@angular/core/testing';
import {
  BrowserDynamicTestingModule,
  platformBrowserDynamicTesting
} from '@angular/platform-browser-dynamic/testing';

declare const require: any;

// First, initialize the Angular testing environment.
getTestBed().initTestEnvironment(
  BrowserDynamicTestingModule,
  platformBrowserDynamicTesting()
);
// Then we find all the tests.
const context = require.context('./', true, /Test-Demo\.spec\.ts$/);
// And load the modules.
context.keys().map(context);

Note: Test-Demo is nothing but Test-Demo.spec.ts.

Step 2

Run ng test --code-coverage 

Now Karma and Jasmine will check only Test-Demo.Spec.ts.

Before you push, you should run all the test cases and don’t push this file to the next repository.

Hope you enjoy. 

Step 3

Run Karma on module base 

const context = require.context('app/module-name/', true, /\.spec\.ts$/);