What is Unit Testing?
Unit Testing is a type of software testing where individual components (units) of a program are tested in isolation to ensure they work as expected. Each unit is tested separately before integrating it into the whole system.
- Performed by: Developers (usually)
- Objective: Identify bugs at an early stage
- Automation Tools: JUnit (Java), NUnit (.NET), PyTest (Python), Jest (JavaScript), Google Test (C++)
Why is Unit Testing Important?
✔ Early Bug Detection → Saves time & cost
✔ Improves Code Quality → Ensures correctness of each function
✔ Easier Refactoring → Allows modification without breaking existing features
✔ Faster Debugging → Pinpoints which module is failing
✔ Supports CI/CD → Ensures smooth automated deployments
Types of Unit Testing
Unit testing can be categorized into two main types:
- Manual Unit Testing
- Automated Unit Testing
However, in modern development, Automated Unit Testing is preferred due to its speed and reliability.
1️⃣ Manual Unit Testing
- Test cases are executed manually without test automation tools.
- Mostly used in early development phases when automation is not set up.
- Not scalable for large applications.
📌 Example: A developer manually runs a Python function in a console to check its output.
2️⃣ Automated Unit Testing
- Uses test scripts and frameworks to validate unit behavior.
- Faster, more reliable, and repeatable than manual testing.
- Essential for Agile & DevOps environments.
📌 Example: Using JUnit to test a “calculateTotalPrice()” function automatically.
Types of Automated Unit Testing
A. White Box Testing (Code-Centric Testing)
- Tests internal logic, paths, and conditions in code.
- Requires knowledge of the internal structure of the code.
- Includes:
- Statement Coverage – Ensures every line of code executes at least once.
- Branch Coverage – Tests all possible if/else or switch conditions.
- Path Coverage – Covers all possible execution flows in a function.
- Loop Testing – Ensures loops behave correctly with various iterations.
📌 Example: Checking if an if-else statement in a function covers all scenarios.
B. Black Box Testing (Behavior-Driven Testing)
- Tests the input/output behavior without checking the internal code structure.
- Ensures the function produces correct results for valid and invalid inputs.
- Common techniques:
- Boundary Value Analysis – Tests extreme input values.
- Equivalence Partitioning – Divides input into valid/invalid groups.
📌 Example: Testing a login function with valid and invalid passwords.
C. Gray Box Testing (Hybrid Testing)
- Combines White Box & Black Box testing approaches.
- The tester knows some internal code but mainly focuses on input/output validation.
- Useful for API Testing and Integration Testing.
📌 Example: Testing how a function interacts with a database (ensuring correct data storage).
Unit Testing Techniques
- Test-Driven Development (TDD) – Write tests before writing code.
- Behavior-Driven Development (BDD) – Focus on system behavior from a user perspective.
- Mocking & Stubbing – Simulate dependencies to isolate the unit being tested.
