🧠 White Box Testing (also known as Clear Box, Glass Box, or Structural Testing) is a method of software testing where the tester has full visibility into the internal workings of the system—including the code, logic, and architecture.

🔍 What Is White Box Testing?

Unlike Black Box Testing, which focuses on inputs and outputs, White Box Testing dives into the code itself to verify:

• Logical flow
• Conditions and loops
• Data structures
• Internal security
• Error handling

It’s like being a mechanic who inspects every part of the engine to ensure it runs smoothly.

🧠 Key Characteristics

• Tester’s Perspective: Developer or someone with programming knowledge
• Focus: Internal logic, structure, and code paths
• Basis: Source code, design documents, and architecture
• Tools Used: Unit testing frameworks (e.g., JUnit, NUnit), code coverage tools

🧪 Common Types of White Box Testing

✅ Example

Suppose you have a function that calculates the square root of a number:

def safe_sqrt(x):
    if x < 0:
        return None
    else:
        return x ** 0.5

White Box Testing would:

• Check both branches of the if statement
• Test with negative, zero, and positive values
• Ensure the return values are correct
• Possibly inspect performance and exception handling

🛡️ Advantages

• Thorough coverage of code paths
• Helps catch hidden logic errors
• Enables optimization and refactoring
• Useful for security and performance testing

⚠️ Limitations

• Requires programming knowledge
• Time-consuming for large systems
• Doesn’t test user experience or external behavior