Code review comment for lp:~jelmer/bzr/foreign-tests

This branch adds two testcase classes in bzrlib.tests.foreign.test_branch that can be used as basis for the testcases in foreign branch plugins. I've posted matching branches of bzr-svn (lp:~jelmer/bzr-svn/foreign-tests and bzr-git (lp:~jelmer/bzr-git/foreign-tests) that use this. I'm hoping to add a lot more (and more complex) generic tests for the foreign code, to avoid duplicate work in each foreign vcs plugin.

I've considered using adapters rather than "manual" subclassing, but since some subclassing will be needed anyway (the generic tests don't test everything that should be tested) I think that would be overkill.

Does this seem like a reasonable approach?