[pitivi] tests_: Avoid TestLayers tests being run twice

[Thibault Saunier <tsaunier src gnome org>]

commit db89ea9ae56984711a3d60004536941da157b91d
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Sat Feb 11 23:24:48 2017 +0100

    tests_: Avoid TestLayers tests being run twice
    
    Reviewed-by: Thibault Saunier <tsaunier gnome org>
    Differential Revision: https://phabricator.freedesktop.org/D1659

 tests/test_undo_timeline.py |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/tests/test_undo_timeline.py b/tests/test_undo_timeline.py
index a8d1776..97f7846 100644
--- a/tests/test_undo_timeline.py
+++ b/tests/test_undo_timeline.py
@@ -37,7 +37,6 @@ from pitivi.undo.undo import PropertyChangedAction
 from pitivi.utils.ui import LAYER_HEIGHT
 from pitivi.utils.ui import URI_TARGET_ENTRY
 from tests import common
-from tests.test_timeline_timeline import TestLayers
 
 
 class BaseTestUndoTimeline(TestCase):
@@ -94,6 +93,9 @@ class BaseTestUndoTimeline(TestCase):
 
     def check_layers(self, layers):
         self.assertEqual(self.timeline.get_layers(), layers)
+        # Import TestLayers locally, otherwise its tests are discovered and
+        # run twice.
+        from tests.test_timeline_timeline import TestLayers
         TestLayers.check_priorities_and_positions(self, self.timeline.ui, layers, list(range(len(layers))))