new_contents: import store_fixture
  import groundstation.store
  
  from groundstation.gref import Gref
  
  
  class TestGitGref(store_fixture.StoreTestCase):
      storeClass = groundstation.store.git_store.GitStore
  
      def test_write_tip(self):
          gref = Gref(self.repo, "testchannel", "test_write_tip")
          gref.write_tip("foobarbaz", "")
          self.assertEqual(list(gref), ["foobarbaz"])
  
subject: Add test for gref writing