'Test the _write_fills() method'

def test_write_fills(self):

    self.styles.fill_count = 2
    self.styles._write_fills()
    exp = '<fills    count="2"><fill><patternFill    patternType="none"/></fill><fill><patternFill    patternType="gray125"/></fill></fills>'
    got = self.fh.getvalue()
    self.assertEqual(got, exp)
