Insights on Fault Interference for Programs with Multiple Bugs

Multiple faults in a program may interact with each other in a variety of ways. A test case that fails due to a fault may not fail when another fault is added, because the second fault may mask the failure-causing effect of the first fault. Multiple faults may also collectively cause failure on a test case that does not fail due to any single fault alone. Many studies try to perform fault localization on multi-fault programs and several of them seek to match a failed test to its causative fault. It is therefore, important to better understand the interference between faults in a multi-fault program, as an improper assumption about test case failure may lead to an incorrect matching of failed test to fault, which may in turn result in poor fault localization. This paper investigates such interference and examines if one form of interference holds more often than another, and uniformly across all conditions. Empirical studies on the Siemens suite suggest that no one form of interference holds unconditionally and that observation of failure masking is a more frequent event than observation of a new test case failure.