mfplat/tests: Test that the content of DXGI buffers is discarded when locking for writing.

dlls/mfplat/tests/mfplat.c

@@ -7442,7 +7442,8 @@ static void test_d3d11_surface_buffer(void)
     ok(hr == S_OK, "Unexpected hr %#lx.\n", hr);
 
     /* Lock flags are honored, so reads and writes are discarded if
-     * the flags are not correct. */
+     * the flags are not correct. Also, previous content is discarded
+     * when locking for writing and not for reading. */
     put_d3d11_texture_color(texture, 0, 0, 0xcdcdcdcd);
     hr = IMF2DBuffer2_Lock2DSize(_2dbuffer2, MF2DBuffer_LockFlags_Read, &data, &pitch, &data2, &length);
     ok(hr == S_OK, "Unexpected hr %#lx.\n", hr);
@@ -7458,6 +7459,14 @@ static void test_d3d11_surface_buffer(void)
     hr = IMF2DBuffer2_Lock2DSize(_2dbuffer2, MF2DBuffer_LockFlags_Write, &data, &pitch, &data2, &length);
     ok(hr == S_OK, "Unexpected hr %#lx.\n", hr);
     ok(*(DWORD *)data != 0xefefefef, "Unexpected leading dword.\n");
+    IMF2DBuffer2_Unlock2D(_2dbuffer2);
+
+    color = get_d3d11_texture_color(texture, 0, 0);
+    ok(color != 0xefefefef, "Unexpected leading dword.\n");
+
+    hr = IMF2DBuffer2_Lock2DSize(_2dbuffer2, MF2DBuffer_LockFlags_Write, &data, &pitch, &data2, &length);
+    ok(hr == S_OK, "Unexpected hr %#lx.\n", hr);
+    ok(*(DWORD *)data != 0xefefefef, "Unexpected leading dword.\n");
     memset(data, 0x89, 4);
     IMF2DBuffer2_Unlock2D(_2dbuffer2);