Add comprehensive unit test suite for Angular2-HN

[devin-ai-integration]

Add comprehensive unit test suite for Angular2-HN

Summary

This PR adds unit tests for all components, services, and pipes in the Angular2-HN application. The project previously had no .spec.ts test files, only placeholder e2e tests. This adds 14 new test files covering the entire application.

Components tested: AppComponent, FeedComponent, ItemComponent, ItemDetailsComponent, CommentComponent, UserComponent, HeaderComponent, FooterComponent, SettingsComponent, LoaderComponent, ErrorMessageComponent

Services tested: HackerNewsAPIService, SettingsService

Pipes tested: CommentPipe

The karma.conf.js was also updated to support headless Chrome for CI environments.

Review & Testing Checklist for Human

• Verify tests pass in CI - Tests could not be run locally due to ChromeHeadless startup issues in the dev environment. The build compiles successfully, but runtime test execution needs verification in CI.
• Review karma.conf.js changes - Changed default browser from Chrome to ChromeHeadless and singleRun from false to true. Confirm this is the desired behavior for the project.
• Check HackerNewsAPIService tests - These tests only verify methods return Observables, not actual HTTP behavior. Consider if deeper testing is needed.
• Verify mocking strategies - Tests use jasmine spies for service mocking. Ensure mocks accurately reflect service interfaces.

Recommended test plan:

1. Wait for CI to run and verify all tests pass
2. If CI has issues with ChromeHeadless, may need to adjust the --no-sandbox and --disable-gpu flags in the ChromeHeadlessCI launcher
3. Optionally run npm test locally to verify tests work in a standard development environment

Notes

• Pre-existing lint errors in source files were not addressed as they are unrelated to the test suite work
• The e2e tests with Protractor were not modified

Link to Devin run: https://app.devin.ai/sessions/d993f1572b614bbaa7e42d5436188931
Requested by: mason.batchelor@cognition.ai (@mbatchelor81)

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