Comment 3 for bug 516183

The way I would suggest handling this is by moving the server into a separate module that depends on testtools but that does not need to be loaded in normal use.

  File ".../bzr.dev/bzrlib/transport/__init__.py", line 1589, in get_transport
    transport, last_err = _try_transport_factories(base, factory_list)
  File ".../bzr.dev/bzrlib/transport/__init__.py", line 1612, in _try_transport_factories
    return factory.get_obj()(base), None
  File ".../bzr.dev/bzrlib/registry.py", line 61, in get_obj
    self._do_import()
  File ".../bzr.dev/bzrlib/registry.py", line 70, in _do_import
    obj = __import__(self._module_name, globals(), locals(), names)
  File ".../bzr.dev/bzrlib/transport/sftp.py", line 890, in <module>
    from bzrlib.tests.stub_sftp import StubServer, StubSFTPServer
  File ".../bzr.dev/bzrlib/tests/__init__.py", line 53, in <module>
    import testtools
ImportError: No module named testtools