'If passed an input file containing a variable access, L{filter} writes
a I{pre} tag containing a I{py-src-variable} span containing the
variable.'

def test_variable(self):

    input = BytesIO('foo\n')
    output = BytesIO()
    filter(input, output)
    self.assertEqual(output.getvalue(), '<pre><span    class="py-src-variable">foo</span><span    class="py-src-newline">\n</span><span    class="py-src-endmarker"></span></pre>\n')
