How many times have you seen tests that resemble the following?
What are the meanings of the literal values
4 in this code? Sure, you can read the documentation, assuming it exists, for
transformIt() and know what it is supposed to do. In the absence of documentation, you can look at the implementation and reverse engineer the code, but then you are testing implementation, not intent. Also, the author of code such as this requires each following developer to decipher his own intent in addition to whatever intent needs to be extracted from the code under test.
Would you rather see something like Listing 5-1 instead?