playlist->add (film, contentB);
Empty black (film, playlist, bind(&has_video, _1), playlist->length(film));
BOOST_REQUIRE_EQUAL (black._periods.size(), 1U);
playlist->add (film, contentB);
Empty black (film, playlist, bind(&has_video, _1), playlist->length(film));
BOOST_REQUIRE_EQUAL (black._periods.size(), 1U);