Unit Testing

Definitions

1. Unit testing is the practice of writing automated tests that verify individual functions, methods, or classes in isolation from the rest of the system. Each test targets a small, specific unit of behavior, typically with external dependencies replaced by mocks or stubs. Unit tests form the base of the testing pyramid: they are fast (milliseconds per test), cheap to maintain, and provide precise feedback about what broke. Popular frameworks include JUnit (Java), pytest (Python), Jest (JavaScript), and xUnit (.NET). A well-tested codebase may have thousands of unit tests that run in seconds, enabling developers to refactor confidently. Unit tests work best for pure logic and algorithms; integration and end-to-end tests cover the gaps where components interact.

   In plain English: Testing one small piece of code at a time, in isolation, to make sure each piece works correctly on its own before combining them.

   Example: "Each pure function gets a unit test. Integration tests cover how they work together."

Related Terms

• Code Coverage
• Test-Driven Development
• Testing
• Mutation Testing
• Namespace
• Shift Left
• Property-Based Testing
• Acceptance Testing
• Assertion
• BDD
• Benchmark Suite
• Breakpoint
• Code Review Bot
• End-to-End Test