  The performance of many Fault Localisation (FL) techniques directly depends
on the quality of the used test suites. Consequently, it is extremely useful to
be able to precisely measure how much diagnostic power each test case can
introduce when added to a test suite used for FL. Such a measure can help us
not only to prioritise and select test cases to be used for FL, but also to
effectively augment test suites that are too weak to be used with FL
techniques. We propose FDG, a new measure of Fault Diagnosability Gain for
individual test cases. The design of FDG is based on our analysis of existing
metrics that are designed to prioritise test cases for better FL. Unlike other
metrics, FDG exploits the ongoing FL results to emphasise the parts of the
program for which more information is needed. Our evaluation of FDG with
Defects4J shows that it can successfully help the augmentation of test suites
for better FL. When given only a few failing test cases (2.3 test cases on
average), FDG can effectively augment the given test suite by prioritising the
test cases generated automatically by EvoSuite: the augmentation can improve
the acc@1 and acc@10 of the FL results by 11.6x and 2.2x on average, after
requiring only ten human judgements on the correctness of the assertions
EvoSuite generates.
