Final answer:
Expected results in software testing should be defined in advance to guide test validation. They are applicable to various testing levels and confirm that the system behaves as intended. The correct answer is that expected results are most useful when specified in advance, not just in system or component testing.
Step-by-step explanation:
The subject of this question pertains to the field of software testing, specifically the use of expected results in various testing scenarios. Expected results are test conditions that are predetermined to ensure a software's functionality matches its requirements.
Option C: most useful when specified in advance, is the correct answer. This concept is essential because specifying expected results in advance allows testers to compare the actual outcomes with what was intended, thereby determining if a feature is functioning as it should. Expected results are not just important in system testing or component testing; they can be applied to various levels of testing, and the validity of these expected results is not derived from the code itself, but from the requirements or design specifications of the software.
When expected results are specified before testing begins, it serves as a guideline for testers to validate the correctness of the system's responses during the test, thereby enabling more reliable and efficient testing processes.