I am neither an expert nor do I know what the reasoning behind the
naming initially was. But my initial thought about your question was
that a single method named tesXXX is actually a test, and the class
containing all these tests is intended to check the assertions that are
formulated in the individual tests. So the TestCase contains a number of
tests and makes sure they can be run and probed.
Not sure this is related to truth in any way, however...
Joachim