'Test the _write_merge_cells() method'

def test_write_merge_cells_3(self):

    cell_format = Format()
    self.worksheet.merge_range('B3:C3', 'Foo', cell_format)
    self.worksheet.merge_range('A2:D2', 'Foo', cell_format)
    self.worksheet._write_merge_cells()
    exp = '<mergeCells    count="2"><mergeCell    ref="B3:C3"/><mergeCell    ref="A2:D2"/></mergeCells>'
    got = self.fh.getvalue()
    self.assertEqual(got, exp)
