GeezerVison

I think some of this and the code above can be folded to use stuff from https://github.com/python/cpython/blob/master/Lib/test/test_importlib/fixtures.py like:

• cpython/Lib/test/test_importlib/fixtures.py

  Lines 71 to 83 in fd5116c

  	class OnSysPath(Fixtures):
  	@staticmethod
  	@contextlib.contextmanager
  	def add_sys_path(dir):
  	sys.path[:0] = [str(dir)]
  	try:
  	yield
  	finally:
  	sys.path.remove(str(dir))
  	def setUp(self):
  	super(OnSysPath, self).setUp()
  	self.fixtures.enter_context(self.add_sys_path(self.site_dir))

• cpython/Lib/test/test_importlib/fixtures.py

  Lines 50 to 56 in fd5116c

  	@contextlib.contextmanager
  	def install_finder(finder):
  	sys.meta_path.append(finder)
  	try:
  	yield
  	finally:
  	sys.meta_path.remove(finder)

The OnSysPath fixture appears to be designed for a unittest test case, not doctest. A standalone version of the add_sys_path context manager might work if combined with install_finder; however, I notice that neither of those clears the path importer cache, and neither one removes the imported test module from sys.modules when the test is done. I don't know enough about the internals of the test framework to know if leaving out those last two items is OK; I put them in to make sure that everything that could possibly be mutated by this particular test was restored afterwards.

This is misnamed as this is implementing a finder and a loader, so call it an importer.

I'll push an update changing the name to TestImporter.

Commit bb836d7 does the name change.