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name: angular-testing description: Write Angular component tests using TestBed, ComponentHarness, and HttpTestingController with proper signal input handling. Use when writing component tests, mocking HTTP calls, or testing signal inputs. metadata: triggers: files: - '**/*.spec.ts' keywords: - TestBed - ComponentFixture - TestHarness - provideHttpClientTesting

Testing

Priority: P1 (HIGH)

Core Philosophy

• Coverage is diagnostic and project-configured; verify risk-weighted critical paths rather than padding code for an arbitrary percentage.

Core Rule Anchors

• [WEB-TEST-01] Tripartite Naming & AAA Cadence: Test names must follow Method_Scenario_ExpectedBehavior and adhere strictly to Arrange-Act-Assert.
• [WEB-TEST-02] Accessible Harnesses & User Actions: Query UI components via ComponentHarness (e.g. MatButtonHarness) or accessible queries; strictly ban raw CSS class selectors or arbitrary DOM traversal.
• [WEB-TEST-03] Ban on Component Private State & Property Inspection: Never inspect component private state or internal properties directly. Assert on visible DOM state, output events, or harness query outcomes.
• [WEB-TEST-04] HTTP Boundary Mocking: Intercept HTTP requests at the boundary using provideHttpClientTesting() + HttpTestingController rather than mocking internal services or methods. Tests must verify true component data flow.
• [WEB-TEST-05] Bug-First Regression Lock: Every PR resolving a bug ticket or with title fix(...) must introduce a test reproducing the defect prior to the fix.

Implementation Guidelines

• Query via Component Harnesses ([WEB-TEST-02]): Use ComponentHarness (e.g. MatButtonHarness) not CSS selectors. loader.getHarness(MatButtonHarness) + await button.click(). Never query by CSS class. See harness pattern.
• Mock HTTP ([WEB-TEST-04]): Intercept with provideHttpClientTesting() + HttpTestingController rather than manual mocks. Call expectOne, .flush(mockData), and verify() in afterEach.
• Signal Inputs ([WEB-TEST-03]): Use fixture.componentRef.setInput('name', value) + fixture.detectChanges(), not direct assignment. Signals sync — no fakeAsync needed for most signal-driven tests.
• Test Runner: Angular v20+ defaults to Vitest via @angular/build:unit-test (faster, native ESM, no Karma). Configure in angular.json. Jasmine/Karma still supported. Standalone: import directly in TestBed.configureTestingModule({ imports: [StandaloneComponent] }).

Anti-Patterns

• [WEB-TEST-01] Vague test names: Banish non-descriptive names or mixed AAA phases; follow Method_Scenario_ExpectedBehavior.
• [WEB-TEST-02] Raw CSS selectors / DOM traversal: Query via ComponentHarness or accessible roles, not CSS class strings.
• [WEB-TEST-03] Testing private state: Never inspect internal properties or use direct @Input() assignment; use setInput().
• [WEB-TEST-04] Manual HttpClient mocks: Always mock the network boundary with provideHttpClientTesting() + HttpTestingController.
• [WEB-TEST-05] Bug fix without reproduction test: Ban bug fix PRs lacking defect regression tests.
• Coverage padding: Never write low-value tests solely to meet an arbitrary percentage.

References

• Harness Pattern

Canonical response anchors

When this skill applies, preserve the following domain terminology or equivalent concrete examples in the answer when relevant:

• Never query by CSS class

• native ESM

• Additional task-grounded exact anchors: ComponentHarness