public List<Example<T>> getData() {
        return Collections.unmodifiableList(data);
    }
@Test
    public void testGetData() {
        OutputFactory<MockOutput> outputFactory = new MockOutputFactory();
        MutableDataset<MockOutput> a = new MutableDataset<>(new MockDataSourceProvenance(), outputFactory);
        Assertions.assertThrows(UnsupportedOperationException.class, () -> a.getData().add(mkExample(outputFactory.generateOutput("1"), "a")), "Expected exception thrown as adding to unmodifiable list.");
    }