@Test
public void testSave_ToWriter() {

    DataFrame df = DataFrame.newFrame("A", "B").foldByRow(
            1, 2,
            3, 4);
    StringWriter out = new StringWriter();
    Csv.saver().save(df, out);
    assertEquals("A,B\r\n" +
            "1,2\r\n" +
            "3,4\r\n", out.toString());
}