Descriptions are implemented as a single class rather than a Composite because
they are entirely informational. They contain no logic aside from counting their tests.
In the past, we used the raw junit.framework.TestCases and junit.framework.TestSuites
to display the tree of tests. This was no longer viable in JUnit 4 because atomic tests no longer have a superclass below Object.
We needed a way to pass a class and name together. Description emerged from this.