'Test the _write_worksheet() method'

def test_write_worksheet(self):

    self.worksheet._write_worksheet()
    exp = '<worksheet    xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main"    xmlns:r="http://schemas.openxmlformats.org/officeDocument/2006/relationships">'
    got = self.fh.getvalue()
    self.assertEqual(got, exp)
