def test_ignore_multi_add(self):
        self.dc.append(self.data)
        self.dc.append(self.data)
        assert len(self.dc) == 1
data only added once, even after multiple calls to append
dataset/ETHPy150Open glue-viz/glue/glue/core/tests/test_data_collection.py/TestDataCollection.test_ignore_multi_add