What is fault masking?
When presence of one defect hides the presence of another defect in the system is known as fault masking.
Example: If the "Negative Value " cause a firing of unhandled system exception,the developer will prevent the negative values input.This will resolve the issue and hide the defect unhandled exception firing.
When the tester or developer masks a fault by creating a test case which conceals the presence of the fault, it is called fault masking.
In fault masking , one error condition hides the occurrence of another error condition.