What should an Angular component test verify?

Tests rendered behavior, user interaction, outputs, and visible failure states without coupling to private implementation details.

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TL;DR

I test the component through its public inputs, rendered output, user interactions, and emitted events. I use TestBed when Angular rendering, dependency injection, or change detection is part of the behavior. I avoid asserting private fields or calling private methods because those tests can pass while the user-facing behavior is broken.

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Angular component testing, TestBed, DOM behavior, public contracts, and test maintainability.

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Answer path

Core answer first, then checkpoints toward a stronger answer.

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Core answer
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Overview
A useful component test proves what a consumer or user can observe, not how the component happens to implement it.
I test the component through its public inputs, rendered output, user interactions, and emitted events. I use TestBed when Angular rendering, dependency injection, or change detection is part of the behavior. I avoid asserting private fields or calling private methods because those tests can pass while the user-facing behavior is broken.
Checkpoint
Stronger answer
Optional upgrade with examples, trade-offs, and sharper phrasing.
For a save panel, I would set its input, click the real button, and verify the disabled, pending, success, and error states plus the output it emits. Dependencies are replaced only at a meaningful boundary, such as an HTTP service, rather than mocking every collaborator. I prefer accessible queries and visible text over CSS classes that exist only for styling. Small pure functions can still have plain unit tests without TestBed.

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Common mistakesCandidateCommon mistakesMistakes that weaken the answer or signal shallow understanding.Open details

Details

Testing private methods instead of observable behavior.
Keeping only the generated component-creation assertion.
Mocking Angular itself until the template and providers are no longer exercised.

What should an Angular component test verify?

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