Testlets are set of tests to apply to a software under test (SUT). Testlets itself contain multiple tests which are run with the provided SUT to see if it meets a bunch of requirements specified through the testlet.

A typical testlet is the {@link net.joala.testlet.TestToString toString() testlet}: It assumes that you want to put all fields of a class into the toString() output and that the classname itself should be mentioned in the resulting output. The testlet verifies these assumptions.