def render_one_frame(anim, filename, config, verbose=True):
    """Export one moment in the animation (for testing)."""
    t = config.t
    t = anim.duration(config) if t is None or t.end is None else t.end
    img = anim.get_cairo_frame(t, config)
    img.write_to_png(filename)
    if verbose:
        print(f'Wrote to: {filename}')
