'Test the _write_merge_cells() method'

def test_write_merge_cells_1(self):

    cell_format = Format()
    self.worksheet.merge_range(2, 1, 2, 2, 'Foo', cell_format)
    self.worksheet._write_merge_cells()
    exp = '<mergeCells    count="1"><mergeCell    ref="B3:C3"/></mergeCells>'
    got = self.fh.getvalue()
    self.assertEqual(got, exp)
