@Test
public void writeToStream() throws Exception {

    StringWriter sb = new StringWriter();
    DataFrame df = new DataFrame();
    String[] col1 = {"a", "b"};
    double[] col2 = {1.0, 2.0};
    df.addColumn("col1", col1);
    df.addColumn("col2", col2);
    CSVDataFrameWriter writer = new CSVDataFrameWriter();
    writer.writeToStream(df, sb);
    String out = sb.toString();
    assertEquals(3, out.split("\n").length);
    assertTrue(out.contains("b"));
}