Raise tooz error when unexpected last entries found

When the file driver is deleting a group, the only
thing left in that group directory should be the
group metadata file, so before deleting the group
add a check that makes sure the leftover file is
actually the metadata file (and not something else).

Change-Id: I63a1e2cf95d524fea5e1c009ecc951670e2e8f5c

tooz/drivers/file.py

@@ -449,6 +449,11 @@ class FileDriver(coordination._RunWatchersMixin,
             else:
                 if len(entries) > 1:
                     raise coordination.GroupNotEmpty(group_id)
+                elif len(entries) == 1 and entries != ['.metadata']:
+                    raise coordination.ToozError(
+                        "Unexpected path '%s' found in"
+                        " group directory '%s' (expected to only find"
+                        " a '.metadata' path)" % (entries[0], group_dir))
                 else:
                     try:
                         shutil.rmtree(group_dir)

tooz/tests/drivers/test_file.py

@@ -15,6 +15,9 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import os
+
+import fixtures
 import mock
 from testtools import testcase
 
@@ -32,6 +35,26 @@ class TestFileDriver(testcase.TestCase):
         coord = coordination.get_coordinator(url, self._FAKE_MEMBER_ID)
         self.assertEqual(file_path, coord._dir)
 
+    def test_leftover_file(self):
+        fixture = self.useFixture(fixtures.TempDir())
+
+        file_path = fixture.path
+        url = 'file://%s' % file_path
+
+        coord = coordination.get_coordinator(url, self._FAKE_MEMBER_ID)
+        coord.start()
+        self.addCleanup(coord.stop)
+
+        coord.create_group(b"my_group").get()
+        safe_group_id = coord._make_filesystem_safe(b"my_group")
+        with open(os.path.join(file_path, 'groups',
+                  safe_group_id, "junk.txt"), "wb"):
+            pass
+        os.unlink(os.path.join(file_path, 'groups',
+                               safe_group_id, '.metadata'))
+        self.assertRaises(coordination.ToozError,
+                          coord.delete_group(b"my_group").get)
+
     @mock.patch('os.path.normpath', lambda x: x.replace('/', '\\'))
     @mock.patch('sys.platform', 'win32')
     def test_base_dir_win32(self):