'Test the _write_cell_style_xfs() method'

def test_write_cell_style_xfs(self):

    self.styles._write_cell_style_xfs()
    exp = '<cellStyleXfs    count="1"><xf    numFmtId="0"    fontId="0"    fillId="0"    borderId="0"/></cellStyleXfs>'
    got = self.fh.getvalue()
    self.assertEqual(got, exp)
