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intermediate Phase · Testing

Test Coverage

Measure and improve test coverage without chasing 100%.

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Test Coverage

Coverage Metrics

Metric Description
Line coverage % of lines executed
Branch coverage % of branches taken
Method coverage % of methods called

Coverage Tools

  • JaCoCo (Java)
  • Istanbul (JavaScript)
  • Coverage.py (Python)

Good Coverage Target

  • 70-80% is reasonable
  • 100% is not always practical
  • Focus on critical paths

Key Points

  • Understanding Test Coverage is essential for production systems
  • Always consider scalability and maintainability
  • Test thoroughly before deploying to production
  • Monitor performance and set up alerting

Common Patterns

  1. Validation: Always validate input at the boundary
  2. Error Handling: Use structured error responses
  3. Logging: Log key events for debugging
  4. Testing: Unit, integration, and load tests
  5. Documentation: Keep docs updated with code changes

Testing Strategies

Testing Pyramid

     /  E2E  \
    /----------\
   / Integration \
  /----------------\
 /      Unit        \
/--------------------

Test Types

  • Unit: Individual components
  • Integration: Component interactions
  • E2E: Full user workflows
  • Performance: Load/stress testing

Best Practices

  • Write tests first (TDD)
  • Aim for 80% coverage
  • Test edge cases
  • Keep tests fast and isolated

Key Points

  • Understanding Test Coverage is essential for production systems
  • Always consider scalability and maintainability
  • Test thoroughly before deploying to production
  • Monitor performance and set up alerting

Common Patterns

  1. Validation: Always validate input at the boundary
  2. Error Handling: Use structured error responses
  3. Logging: Log key events for debugging
  4. Testing: Unit, integration, and load tests
  5. Documentation: Keep docs updated with code changes

Practice Problems

0 / 3 solved
Implement Test Coverage

Design and implement a solution for Test Coverage in a backend system. Consider scalability, error handling, and production readiness.

Solution 
// Test Coverage implementation
// Key aspects: validation, error handling, logging, testing

public class TestCoverage {
    // Production-ready implementation
}
Test Coverage Edge Cases

Identify and handle edge cases for Test Coverage. What happens under high load, with invalid input, or during failures?

Solution 
// Edge case handling:
// 1. Null/empty input -> validation
// 2. High load -> rate limiting, queuing
// 3. Failures -> retries, circuit breaker
// 4. Concurrent access -> locks, idempotency
Test Coverage Testing Strategy

Write a testing strategy for Test Coverage. Include unit tests, integration tests, and performance tests.

Solution 
// Test plan:
// - Unit: 80% coverage target
// - Integration: API contracts
// - Performance: latency, throughput
// - Chaos: failure injection

Quiz

1. 100% test coverage means?

Question 1 options

2. Good coverage target?

Question 2 options

3. What is a common mistake when implementing Test Coverage?

Question 3 options

Flashcards

Question

100% coverage guarantee?

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Answer

No - all lines executed, not necessarily correct

Question

Good target?

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Answer

70-80% (focus on critical paths)

Question

Test Coverage best practices

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Answer

Follow SOLID principles, write clean code, test thoroughly, document decisions, and monitor in production.

Revision Notes

Key Takeaways

  • 1. Coverage measures executed code percentage
  • 2. 100% coverage does not mean correct code
  • 3. 70-80% is reasonable
  • 4. Focus on critical paths, not just numbers

Interview Tips

  • • Measure and improve coverage
  • • Know coverage limits

Cheat Sheet

Test Coverage

  • Measures: lines, branches, methods
  • 100% ≠ correct code
  • Target: 70-80%
  • Focus: critical paths, not just numbers