Definition
Unit testing is a software testing method where individual units or components of a software application are tested in isolation from the rest of the system. A unit is typically the smallest testable part of an application, such as a function, method, or class.
Key Characteristics
- Isolation: Tests run independently without dependencies on external systems, databases, or network calls
- Fast execution: Should run quickly (milliseconds to seconds) to enable frequent execution
- Deterministic: Same input should always produce the same output
- Automated: Can be run automatically as part of build processes
- Fine-grained: Tests specific functionality at the smallest possible scope
Benefits
- Early bug detection: Catches issues at the component level before integration
- Refactoring safety: Provides confidence when modifying code
- Documentation: Tests serve as executable specifications of expected behavior
- Design feedback: Writing tests often reveals design issues in the code
Best Practices
- Follow the AAA pattern: Arrange, Act, Assert
- One assertion per test when possible
- Use descriptive test names that explain the scenario and expected outcome
- Keep tests independent - no shared state between tests
- Use Test Doubles when dependencies are needed
Common Frameworks
- Python: pytest, unittest
- JavaScript: Jest, Mocha, Vitest
- Java: JUnit, TestNG
- C#: NUnit, xUnit