White Box Testing

White Box Testing refers to the technique of testing a system with knowledge of the internals of the system. White Box testers have access to the source code and are aware of the system architecture. A White Box tester typically analyzes source code, derives test cases from knowledge about the source code, and finally targets specific code paths to achieve a certain level of code coverage. A White Box tester with access to details about both operations can readily craft efficient test cases that exercise boundary conditions.

Advantages

a. Increased Effectiveness — Crosschecking design decisions and assumptions against source code may outline a robust design, but the implementation may not align with the design intent.
b. Full Code Pathway Capable — all the possible code pathways can be tested including error handling, resource dependencies, and additional internal code logic/flow.
c. Early Defect Identification — Analyzing source code and developing tests based on the implementation details enables testers to find programming errors quickly.
d. Reveal Hidden Code Flaws — access to source code improves understanding and uncovering unintended hidden behavior of program modules.

Disadvantages

a. Difficult To Scale — requires intimate knowledge of target system, testing tools and coding languages, and modeling. It suffers for scalability of skilled and expert testers.
b. Difficult to Maintain — requires specialized tools such as source code analyzers, debuggers, and fault injectors.
c. Cultural Stress — the demarcation between developer and testers starts to blur which may become a cultural stress.
d. Highly Intrusive — requires code modification has been done using interactive debuggers, or by actually changing the source code. This may be adequate for small programs; however, it does not scale well to larger applications. Not useful for networked or distributed systems.