title: How to mock environment files import in unit tests
body: <p>In our angular app, we use environment files to load some config. </p>
  
  <p>environment.ts</p>
  
  <pre><code>export const environment = {
    production: false,
    defaultLocale: 'en_US',
  };
  </code></pre>
  
  <p>We then use it in one of our service:</p>
  
  <pre><code>import { environment } from '../../environments/environment';
  import { TranslateService } from './translate.service';
  
  @Injectable()
  export class LocaleService {
    constructor(private translateService: TranslateService){}
  
    useDefaultLocaleAsLang(): void {
      const defaultLocale = environment.defaultLocale;
      this.translateService.setUsedLang(defaultLocale);
    }
  }
  </code></pre>
  
  <p>So I use the values in environment file in a service method.</p>
  
  <p>In our test file, we can of course Spy on the translateService:</p>
  
  <p><code>translateService = jasmine.createSpyObj('translateService', ['setUsedLang']);</code></p>
  
  <p>But I don't know how to mock the environment values in my testing file (in a <code>beforeEach</code> for example). Or even transform it, for testing purpose, to a <code>Subject</code> so I can change it and test different behaviors.</p>
  
  <p>More generally speaking, how can you mock such imports values in tests to be sure not to use real values? </p>