This class is used by the framework to define the interface of a test
listener. It is an abstract base class implemented by the test
Due to the nature of the Perl OO implementation, this class is not
really needed, but rather serves as documentation of the interface.
Each of the add_ methods gets two arguments: test and exception.
The test is a Test::Unit::Test and the exception is a
Test::Unit::Exception. Typically you want to display
test->name() and keep the rest as details.