ectedFirstSB,
                            "first SourceBuffer matches expectation");
                          assert_equals(mediaSource.sourceBuffers[1], expectedSecondSB,
                            "second SourceBuffer matches expectation");
                          test.expectEvent(mediaSource.activeSourceBuffers, "addsourcebuffer");
                          test.expectEvent(mediaSource.activeSourceBuffers, "addsourcebuffer");
                          test.expectEvent(mediaElement, "loadedmetadata");