public <T extends Output<T>> void save(Path csvPath, Dataset<T> dataset, String responseName) throws IOException {
        save(csvPath, dataset, Collections.singleton(responseName));
    }
@Test
    public void testSaveEmpty() throws IOException {
        MutableDataset<MockOutput> src = new MutableDataset<>(null, new MockOutputFactory());
        CSVSaver saver = new CSVSaver();
        Path tmp = Files.createTempFile("foo-empty","csv");
        tmp.toFile().deleteOnExit();
        saver.save(tmp, src, "RESPONSE");
        CSVLoader<MockOutput> loader = new CSVLoader<>(new MockOutputFactory());
        MutableDataset<MockOutput> tgt = loader.load(tmp, "RESPONSE");
        assertEquals(0, tgt.size());
    }