                     assert_equals(mediaSource.activeSourceBuffers.length, 1,
                            "audio source buffer no longer in the activeSourceBuffers list");
                          assert_equals(mediaSource.activeSourceBuffers[0], sourceBufferVideo,
                            "activeSourceBuffers list only contains the video SourceBuffer");

                          test.expectEvent(mediaSource.activeSourceBuffers, "addsourcebuffer");
                          test.expectEvent(mediaSource