A program can operate incorrectly but still appear to pass your test because (choose correct answer from the following):
The test is automated and it is not programmed to compare the specific misbehavior to an expected result.
The test is manual (run by a human) but the human is paying attention to other aspects of the program's behavior and doesn't notice the misbehavior.
The tester knows how to run the test but doesn't know what to look for as a result.
option1 and 2
All of the above