[pitivi] timeline: fixes traceback on clip adding overlap

[Alexandru Băluț <alexbalut src gnome org>]

commit ed9b35960f9b2aeaac6ceee44884689d71cfd5bb
Author: Vivek R <123vivekr gmail com>
Date:   Sat Jan 18 19:21:40 2020 +0530

    timeline: fixes traceback on clip adding overlap
    
    Fixes #2410

 pitivi/timeline/timeline.py     |  3 +++
 tests/test_timeline_timeline.py | 48 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+)
---
diff --git a/pitivi/timeline/timeline.py b/pitivi/timeline/timeline.py
index 6d24b069..d6e22b6b 100644
--- a/pitivi/timeline/timeline.py
+++ b/pitivi/timeline/timeline.py
@@ -949,6 +949,9 @@ class Timeline(Gtk.EventBox, Zoomable, Loggable):
                                            0,
                                            clip_duration,
                                            asset.get_supported_formats())
+            if not ges_clip:
+                return False
+
             placement += clip_duration
             ges_clip.first_placement = True
             self._project.pipeline.commit_timeline()
diff --git a/tests/test_timeline_timeline.py b/tests/test_timeline_timeline.py
index 0e77d79f..e094302c 100644
--- a/tests/test_timeline_timeline.py
+++ b/tests/test_timeline_timeline.py
@@ -26,6 +26,7 @@ from gi.repository import Gtk
 from pitivi.utils.timeline import UNSELECT
 from pitivi.utils.ui import LAYER_HEIGHT
 from pitivi.utils.ui import SEPARATOR_HEIGHT
+from pitivi.utils.ui import URI_TARGET_ENTRY
 from tests import common
 
 THIN = LAYER_HEIGHT / 2
@@ -821,3 +822,50 @@ class TestClipsEdges(BaseTestTimeline):
         self.assertEqual(timeline_container.first_clip_edge(before=10), 5)
         self.assertEqual(timeline_container.first_clip_edge(before=11), 10)
         self.assertEqual(timeline_container.first_clip_edge(before=20), 15)
+
+
+class TestDragFromOutside(BaseTestTimeline):
+
+    def test_adding_overlap_clip(self):
+        """Checks asset drag&drop on top of an existing clip."""
+        timeline_container = common.create_timeline_container()
+        timeline_ui = timeline_container.timeline
+
+        asset = GES.UriClipAsset.request_sync(
+            common.get_sample_uri("tears_of_steel.webm"))
+        layer, = timeline_ui.ges_timeline.get_layers()
+        layer.add_asset(asset, 0, 0, 10, GES.TrackType.UNKNOWN)
+
+        # Events emitted while dragging an asset over a clip in the timeline:
+        # motion, receive, motion.
+        with mock.patch.object(Gdk, "drag_status") as _drag_status_mock:
+            with mock.patch.object(Gtk, "drag_finish") as _drag_finish_mock:
+                target = mock.Mock()
+                target.name.return_value = URI_TARGET_ENTRY.target
+                timeline_ui.drag_dest_find_target = mock.Mock(return_value=target)
+                timeline_ui.drag_get_data = mock.Mock()
+                timeline_ui._drag_motion_cb(None, None, 0, 0, 0)
+                self.assertTrue(timeline_ui.drag_get_data.called)
+
+                self.assertFalse(timeline_ui.drop_data_ready)
+                selection_data = mock.Mock()
+                selection_data.get_data_type = mock.Mock(return_value=target)
+                selection_data.get_uris.return_value = [asset.props.id]
+                self.assertIsNone(timeline_ui.drop_data)
+                self.assertFalse(timeline_ui.drop_data_ready)
+                timeline_ui._drag_data_received_cb(None, None, 0, 0, selection_data, None, 0)
+                self.assertEqual(timeline_ui.drop_data, [asset.props.id])
+                self.assertTrue(timeline_ui.drop_data_ready)
+
+                timeline_ui.drag_get_data.reset_mock()
+                self.assertIsNone(timeline_ui.dragging_element)
+                self.assertFalse(timeline_ui.dropping_clips)
+
+                # Drag on the first layer.
+                def translate_coordinates_func(widget, x, y):
+                    return x, y
+                timeline_ui.translate_coordinates = translate_coordinates_func
+                timeline_ui._drag_motion_cb(timeline_ui, None, 0, SEPARATOR_HEIGHT, 0)
+                self.assertFalse(timeline_ui.drag_get_data.called)
+                self.assertIsNone(timeline_ui.dragging_element)
+                self.assertFalse(timeline_ui.dropping_clips)