o in the contextualize method where we are getting a reference to the container but we only need the basis PlexusContainer. The only place we need the artifact enabled container is in the addPlugin method. Otherwise, in standard PlexusTestCases we will get a ClassCastException. You do not need to use an ArtifactEnabledTestCase unless you actually want to use the facilities of the artifact enabled container.
maven/components/trunk/maven-core/src/main/java/org/apache/maven/plugin/DefaultPluginManager.java