Fix test using .ndarray and .reformat

Due to differences in current memory reference methods, frames created using .from_ndarray or .reformat are not supported by __dlpack__.

Author: caffeinism

tests/test_dlpack.py

@@ -230,30 +230,34 @@ def test_video_frame_from_dlpack_p010_p016_cpu(fmt: str) -> None:
 
 
 def test_video_plane_dlpack_export_keeps_frame_alive_after_gc() -> None:
-    container = av.open(fate_png())
-    frame = next(container.decode(video=0))
-    frame_nv12 = frame.reformat(format="nv12")
+    width, height = 64, 48
+    frame = VideoFrame(width, height, "nv12")
 
-    width = frame_nv12.width
-    height = frame_nv12.height
-    line_size = frame_nv12.planes[0].line_size
-    expected = _plane_to_2d(frame_nv12.planes[0], height, width, numpy.uint8).copy()
+    y_bytes = numpy.arange(frame.planes[0].buffer_size, dtype=numpy.uint8).tobytes()
+    frame.planes[0].update(y_bytes)
 
-    y_dl = numpy.from_dlpack(frame_nv12.planes[0])
-    assert y_dl.shape == (height, width)
-    assert y_dl.strides == (line_size, 1)
+    y_dl = numpy.from_dlpack(frame.planes[0])
+    expected = y_dl.copy()
 
-    del frame_nv12
     del frame
-    del container
     gc.collect()
 
     assertNdarraysEqual(y_dl, expected)
 
 
-def test_video_plane_dlpack_unsupported_format_raises() -> None:
+def test_video_plane_dlpack_requires_refcounted_frame() -> None:
+    # TODO: By extending `from_dlpack` to implement all pixel formats
+    #       of `from_ndarray`, the issue can be resolved by calling
+    #       `from_dlpack(np.array)` internally within `from_ndarray`.
     rgb = numpy.zeros((16, 16, 3), dtype=numpy.uint8)
     frame = VideoFrame.from_ndarray(rgb, format="rgb24")
+
+    with pytest.raises(TypeError, match="refcounted AVFrame"):
+        frame.planes[0].__dlpack__()
+
+
+def test_video_plane_dlpack_unsupported_format_raises() -> None:
+    frame = VideoFrame(16, 16, "rgb24")
     assert frame.planes[0].__dlpack_device__() == (1, 0)
 
     with pytest.raises(