test: Check clip positioning works when specifying track size

Make use of the new 'timeline specification' support in .validatetest
files.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-editing-services/-/merge_requests/227>

tests/check/meson.build

@@ -88,6 +88,7 @@ if gstvalidate_dep.found()
     'edit_while_seeked_with_stop': true,
     'complex_effect_bin_desc': true,
     'check_keyframes_in_compositor_two_sources': true,
+    'check-clip-positioning': true,
   }
 
   foreach scenario, is_validatetest: scenarios

tests/check/scenarios/check-clip-positioning.validatetest

@@ -0,0 +1,12 @@
+meta,
+    tool = "ges-launch-$(gst_api_version)",
+    handles-states=true,
+    args = {
+        +test-clip, blue, "d=0.5", "asset-id=time-overlay, width=640, height=360, max-duration=5.0", "name=clip",
+        --track-types, video,
+        --videosink, "$(videosink) name=videosink sync=true",
+        --video-caps, "video/x-raw,format=I420,width=640,height=360,framerate=10/1,chroma-site=mpeg2,colorimetry=bt709;",
+    }
+
+check-child-properties, element-name=clip, width=0, height=0
+stop