A test group applied to an annotation indicates that a given annotation
can be used on individual tests as "labels". The meaning of these labels is
mostly application-specific (example:
Nightly
which indicates slower,
more intensive tests that are skipped during regular runs).
RandomizedRunner
collects groups from all tests in a suite. A group
can be enabled or disabled using boolean system properties (or test
hooks in the code). A test case is executed if it has no groups or if all of its groups
are enabled.