angular-testing-best-practices

name	angular-testing-best-practices
description	Use this skill when writing, structuring, or refactoring tests in Angular applications to ensure reliability, maintainability, and coverage.

When testing Angular applications:

1. Follow testing levels:

   • unit tests → components, services, pipes
   • integration tests → component + template interaction
   • e2e tests → full user flows

2. Test components by:

   • focusing on behavior, not implementation
   • using TestBed for setup
   • mocking dependencies via providers
   • testing Inputs/Outputs explicitly
   • avoiding real HTTP calls

3. Test services by:

   • isolating logic
   • mocking external dependencies (HttpClient, other services)
   • verifying inputs and outputs
   • covering edge cases and error handling

4. Use Angular testing utilities:

   • TestBed for dependency injection
   • ComponentFixture for DOM interaction
   • fakeAsync/tick for async control
   • waitForAsync for async setup

5. Mock dependencies using:

   • Jasmine spies or Jest mocks
   • dependency injection overrides
   • HttpTestingController for HTTP requests

6. Test data flow:

   • verify @Input changes update the view
   • verify @Output emits correct events
   • ensure no hidden state mutations

7. Structure tests as:

   • Arrange → setup inputs and mocks
   • Act → trigger behavior
   • Assert → verify results

8. Keep tests:

   • deterministic (no randomness)
   • isolated (no shared state)
   • fast (avoid unnecessary rendering)

9. Avoid:

   • testing internal implementation details
   • relying on real APIs or timers
   • overly complex test setups
   • duplicated test logic

10. Use test doubles appropriately:

    • mocks → verify interactions
    • stubs → provide controlled data
    • spies → track calls and arguments

11. Cover critical scenarios:

    • success paths
    • error handling
    • edge cases
    • invalid inputs
    • boundary conditions
    • unexpected states

12. Never test only the happy path:

    • always include failure scenarios
    • validate error handling behavior
    • simulate API failures and timeouts
    • test defensive logic and fallbacks

13. For HTTP testing:

    • use HttpTestingController
    • assert request method, URL, payload
    • flush mock responses (success and error)

14. For reactive code:

    • test observables with controlled emissions
    • verify subscriptions and side effects
    • test error emissions and completion
    • avoid unhandled async behavior

15. Maintain test quality:

    • keep tests readable and simple
    • use descriptive test names
    • refactor tests alongside code changes

16. Ensure:

    • high coverage on business logic
    • confidence in refactoring
    • alignment with application architecture

If a test only validates the happy path and ignores failures, edge cases, or invalid inputs, it violates this skill.