er == 'imagemagick' and html == 'html5'
            # ImageMagick delegates to ffmpeg for this format.
            and not animation.FFMpegWriter.isAvailable()):
        pytest.skip('Requires FFMpeg')
    # create here rather than in the fixture otherwise we get __del__ warnings
    # about producing no output
    anim = animation.FuncAnimation(**anim)
    with plt.rc_context({'animation.writer': writer,
                         'animation.html': html}):
        html = anim._repr_html_()
    if want is None:
        assert html is None
        with pytest.warns(UserWarning):
            del anim  # Animation was never run, so will warn on cleanup.
            np.testing.break_cycles()
    else:
        assert want in html


@pytest.mark.parametrize(
    'anim',
    [{'save_count': 10, 'frames': iter(range(5))}],
    indirect=['anim']
)
def test_no_length_frames(anim):
    anim.save('unused.null', writer=NullMovieWriter())


def test_movie_writer_registry():
    assert len(animation.writers._registered) > 0
    mpl.rcParams['animation.ffmpeg_path'] = "not_available_ever_xxxx"
    assert not animation.writers.is_available("ffmpeg")
    # something guaranteed to be available in path and exits immediately
    bin = "true" if sys.platform != 'win32' else "where"
    mpl.rcParams['animation.ffmpeg_path'] = bin
    assert animation.writers.is_available("ffmpeg")


@pytest.mark.parametrize(
    "method_name",
    [pytest.param("to_html5_video", marks=pytest.mark.skipif(
        not animation.writers.is_available(mpl.rcParams["animation.writer"]),
        reason="animation writer not installed")),
     "to_jshtml"])
@pytest.mark.parametrize('anim', [dict(frames=1)], indirect=['anim'])
def test_embed_limit(method_name, caplog, tmpdir, anim):
    caplog.set_level("WARNING")
    with tmpdir.as_cwd():
        with mpl.rc_context({"animation.embed_limit": 1e-6}):  # ~1 byte.
            getattr(anim, method_name)()
    assert len(caplog.rec