@Test
public void testAggMultiple() {

    DataFrame aggregated = Series.forData("a", "b", "cd", "e", "fg")
            .group((String s) -> s.length())
            .aggMultiple(
                    SeriesAggregator.first(),
                    SeriesAggregator.concat("|"),
                    SeriesAggregator.concat("_"));
    new DataFrameAsserts(aggregated, "first", "concat", "concat_")
            .expectHeight(2)
            .expectRow(0, "a", "a|b|e", "a_b_e")
            .expectRow(1, "cd", "cd|fg", "cd_fg");
}