DirsOnSysPath doesn't clear sys.path_importer_cache, so it seems you'd always want to use import_state, which does clear it.

We might also want to modify import_state to remember the original objects, not just their values. DirsOnSysPath does do this, for sys.path.

If we do this, we should probably move import_state to test.support.

Also, couldn't import_state do with sys.modules what DirsOnSysPath does with sys.path? It could restore both the object and its contents.