I honestly wouldn't have done this - invoker tests are really only needed where you expect to have build-failing errors that would cause the whole build to fail (not just the part of hte build you're asserting should fail) so you run a sub-build so you can test that build failure separately.  

Though there's no harm in this, except for the cost of a maven invocation.  If you plan on porting these tests over to compiler-testing, then it's probably not a horrible code-organization step.  But I think unnecessary, given how these particular tests are structured.