'Test the _write_num_fmts() method'

def test_write_num_fmts(self):

    xf_format = Format()
    xf_format.num_format_index = 164
    xf_format.set_num_format('#,##0.0')
    self.styles._set_style_properties([[xf_format], None, 0, 1, 0, 0, [], []])
    self.styles._write_num_fmts()
    exp = '<numFmts    count="1"><numFmt    numFmtId="164"    formatCode="#,##0.0"/></numFmts>'
    got = self.fh.getvalue()
    self.assertEqual(got, exp)
