What is the concept of introducing a small change to the program and having the effects of that change show up in some test?

Introducing a small change to the program and observing the effects of that change in some test is known as introducing mutations. This concept is often related to mutation testing, which is a technique used in software testing to evaluate the quality of test cases. It involves making small, intentional modifications to the code (mutations) to see if the existing tests can catch the errors introduced by those changes.

The purpose of mutation testing is to determine how well the tests can detect changes that might lead to faults, thereby assessing the effectiveness of the test suite. If the tests fail when a mutation is introduced, it indicates that the tests are robust enough to catch errors. Conversely, if tests pass despite the mutations, it suggests that the test suite may need improvements to cover such scenarios effectively.

Other options presented do not align with this concept. Performance testing focuses on evaluating how a system performs under various conditions, while debugging involves identifying and fixing bugs rather than introducing changes to see their effects. A mutation error is a term that might describe an error introduced by mutation testing but does not capture the broader concept of testing the effects of intentional changes in software.