White box testing, also known as clear box, glass box, or structural testing, is a software testing method where the internal structures or workings of an application are examined and tested. In this approach, testers have full visibility into the software’s architecture, design, and source code. The goal is to validate the correctness of the code and ensure that all code paths are tested.

Key Aspects of White Box Testing:

  1. Internal Focus: Involves looking at the program’s internal logic and structure.
  2. Knowledge Required: Testers need a deep understanding of the code as they’re required to design test cases based on the application’s architecture and source code.
  3. Comprehensive Testing: Can achieve higher coverage by ensuring that every individual path and branch in the code is tested.

Types of White Box Testing:

  1. Statement Coverage: Ensures each statement in the code is executed at least once.
  2. Branch/Decision Coverage: Guarantees that each decision point (like “if” and “else” statements) is executed for both true and false conditions.
  3. Path Coverage: Tests every possible path through the software.
  4. Loop Testing: Specifically focuses on the validity of loop constructs in the software.
  5. Control Flow Testing: Evaluates the order in which different parts of the code get executed.
  6. Data Flow Testing: Focuses on variable values and tracks the path variables take through the program’s logic.

Advantages:

  1. High Coverage: Has the potential to uncover a majority of the flaws in the code.
  2. Early Bug Detection: As it’s based on the application’s source code, it can be implemented in the initial development phases, catching bugs early.
  3. Helps in Code Optimization: By understanding the code’s behavior, developers can optimize the code for better performance.

Limitations:

  1. Time-Consuming: Given its comprehensive nature, it can be time-intensive.
  2. Requires Expertise: Testers need a deep understanding of the application’s logic and code, which may not always be feasible.
  3. Doesn’t Always Reflect Real-World Use: While it ensures that every part of the code is tested, it might not account for real-world scenarios where certain code paths are rarely or never executed.

Conclusion:

White box testing provides an in-depth evaluation of the software, ensuring the correct functionality of its internal structures. It complements black box testing, which focuses on testing the software from an end-user’s perspective without knowledge of its internal workings. Together, they offer a comprehensive approach to software testing, ensuring both functionality and code correctness.