This principle, though obvious, when overlooked is the cause of
one of the most frequent mistakes in program testing. Again, it is
something that is based on human psychology. If the expected result
of a test case has not been predefined, chances are that a plausible,
but erroneous, result will be interpreted as a correct result because of
the phenomenon of ‘‘the eye seeing what it wants to see.’’ In other
words, in spite of the proper destructive definition of testing, there is
still a subconscious desire to see the correct result. One way of