Test-Driven Development (TDD) for Frontend Engineers Quiz

Explore key principles of Test-Driven Development applied to frontend engineering with this focused quiz. Strengthen your understanding of writing effective, reliable tests, iterative coding, and best practices in frontend TDD workflows.

1. Understanding the TDD Cycle

   What is the correct sequence of steps in the test-driven development (TDD) cycle for frontend features?

   1. Write a failing test, make the test pass, refactor the code
   2. Design the UI, implement the code, write the test
   3. Refactor the code, write the test, implement the feature
   4. Write the code, optimize, document

   Explanation: The correct TDD cycle starts by writing a failing test, implementing just enough code to pass it, and then refactoring. This ensures development is driven by requirements. Designing the UI or implementation first (Option B) ignores the test-first aspect. Refactoring before testing and implementation (Option C) is out of order. Writing code and then documenting or optimizing (Option D) does not follow TDD principles.

2. Benefits of TDD in Frontend Projects

   How does TDD improve maintainability in frontend projects featuring interactive components?

   1. By reducing code branching complexity
   2. By eliminating the need for manual visual checks
   3. By ensuring changes are always covered by automated tests
   4. By automatically optimizing performance

   Explanation: TDD helps maintainability by requiring tests for every change, catching regressions early. While it doesn't eliminate the need for manual checks (Option B), it reduces but does not remove accidental issues. Reducing code branching complexity (Option C) is not a direct benefit of TDD, and performance optimization (Option D) is a separate concern.

3. Types of Tests in TDD

   Which type of test is most appropriate as the first step when applying TDD to a new button component that triggers a modal dialog?

   1. Unit test
   2. End-to-end test
   3. Integration test
   4. Snapshot test

   Explanation: A unit test is the best first step in TDD for a new component, focusing on its individual behavior. Integration tests assess larger flows involving multiple components, which is often premature. End-to-end tests cover user journeys but aren't typically used first in TDD. Snapshot tests check rendered output but do not verify logic or user interaction directly.

4. Common Pitfalls in Frontend TDD

   In a TDD workflow, what is a common mistake when refactoring frontend components after passing tests?

   1. Mocking external APIs
   2. Changing implementation without re-running tests
   3. Removing passing tests for simplicity
   4. Adding features before tests are written

   Explanation: If you refactor without re-running tests, you risk breaking features unnoticed; rerunning tests ensures everything still works as expected. Removing passing tests (Option B) undermines the reliability of your codebase. Adding features before writing tests (Option C) breaks the TDD workflow but is not restricted to the refactoring phase. Mocking APIs (Option D) is a valid practice for isolating tests and not a mistake.

5. TDD and UI Regression

   If a front-end engineer relies solely on TDD-driven unit tests, what risk remains regarding changes that unintentionally alter visual layouts?

   1. Unit tests always prevent CSS issues
   2. Unit tests may not catch visual regressions in the UI
   3. All visual changes will always be detected
   4. It eliminates the need for reviewing pull requests

   Explanation: Unit tests focus on business logic and behavior, often missing unintended layout changes or CSS issues. It's incorrect to claim all visual changes will be detected (Option B). Code review (Option C) and additional UI regression tests are still important. Unit tests do not inherently guard against CSS or layout errors (Option D).