Fault Masking is:

Fault masking refers to situations where one error condition prevents the detection of another error condition. This typically occurs in complex software systems where multiple defects can coexist. When a fault is masked, it means that the presence of one fault obscures or delays the visibility of another fault during testing or operation, potentially leading to a scenario where a bug goes unnoticed.

In practical terms, this can happen when an error triggers an unexpected behavior that takes precedence, causing a different underlying defect to remain hidden. For example, if a fault in the code causes a program to crash, the developer or tester may not realize that a separate, unrelated fault is also present, as the masking fault has already interrupted potential exploration or observation of system behavior.

This concept is vital for testers to understand, as it emphasizes the importance of strategic testing approaches that can reveal such hidden faults, ensuring that the quality of the software is not compromised by overlooked issues. Recognizing fault masking also encourages the practice of thorough regression testing and diversifying testing techniques to uncover all existing defects.