'Test the _write_xf() method. Horizontal alignment = fill.'

def test_write_xf_16(self):

    xf_format = Format()
    xf_format.set_align('fill')
    self.styles._write_xf(xf_format)
    exp = '<xf    numFmtId="0"    fontId="0"    fillId="0"    borderId="0"    xfId="0"    applyAlignment="1"><alignment    horizontal="fill"/></xf>'
    got = self.fh.getvalue()
    self.assertEqual(got, exp)
