human
Here's a good function header given the following:
I wrote the below code

    def mock_kpsewhich(filename):
        nt.assert_equal(filename, 'breqn.sty')
        return None
    for (s, wrap) in [(u'$$x^2$$', False), (u'x^2', True)]:
        (yield (latextools.latex_to_png_dvipng, s, wrap))
        with patch.object(latextools, 'kpsewhich', mock_kpsewhich):
            (yield (latextools.latex_to_png_dvipng, s, wrap))

What's a good function header?
assistant
#Here's a good function header.

@onlyif_cmds_exist('latex', 'dvipng')
def test_latex_to_png_dvipng_runs():