Software Testing - White Box Testing

1. What is White Box Testing?

White Box Testing (also called Clear Box Testing, Structural Testing, or Glass Box Testing) is a software testing technique where the internal structure, logic, and code of the application are known to the tester.

Instead of just checking if the software works (black box), you’re looking inside and verifying that:

  • The code follows the intended logic.

  • All possible execution paths are tested.

  • There are no hidden errors in data flow, conditions, or loops.

2. Key Characteristics

  • Code-based – Requires knowledge of programming and system architecture.

  • Logic-driven – Focuses on conditions, loops, and decision points.

  • Coverage-oriented – Aims to maximize test coverage (statements, branches, paths).

3. Goals of White Box Testing

  • Verify all code paths work as intended.

  • Identify logical errors and hidden bugs.

  • Ensure all conditions and loops are handled properly.

  • Optimize code performance and security.

4. Techniques Used in White Box Testing

1. Statement Coverage

  • Ensures every line of code is executed at least once.

2. Branch Coverage

  • Ensures each decision point (if/else, switch cases) is tested.

3. Path Coverage

  • Ensures all possible execution paths are tested.

4. Condition Coverage

  • Ensures each boolean condition evaluates to both true and false during testing.

5. Loop Testing

  • Tests loops for zero iterations, one iteration, and multiple iterations.

6. Data Flow Testing

  • Checks the proper use of variables (declaration, assignment, usage).

5. Steps to Perform White Box Testing

  1. Understand the code – Review the source code and logic.

  2. Identify testable areas – Look for decision points, loops, conditions.

  3. Design test cases – Based on code paths and conditions.

  4. Prepare the test environment – Set up tools and debugging configurations.

  5. Execute tests – Run tests manually or with automation.

  6. Record results – Log passed/failed cases.

  7. Fix & retest – Developers fix issues, then retesting is done.

6. Tools for White Box Testing

  • JUnit / NUnit – Unit testing frameworks for Java/.NET.

  • CppUnit – Unit testing for C++.

  • PyTest / unittest – Python testing frameworks.

  • SonarQube – Code quality and coverage analysis.

  • EclEmma / JaCoCo – Java code coverage tools.

7. Advantages

  • Finds hidden logical errors.

  • Ensures maximum code coverage.

  • Improves code quality and performance.

  • Helps in early detection of bugs.

8. Disadvantages

  • Requires programming knowledge.

  • Time-consuming for large applications.

  • May miss high-level functional issues.

  • Not effective without complete access to source code.

9. Example

Imagine you have this function:

def check_discount(age):
    if age < 18:
        return "Child discount"
    elif age >= 60:
        return "Senior discount"
    else:
        return "No discount"

White Box Testing would create test cases to ensure:

  • Path 1: age = 10 → returns "Child discount"

  • Path 2: age = 65 → returns "Senior discount"

  • Path 3: age = 30 → returns "No discount"

This way, all branches are covered.

If you’d like, I can create a side-by-side comparison chart of White Box vs Black Box vs Grey Box Testing, so you can clearly see the differences in scope, approach, and skills needed.