@Test
public void testFoldLongStreamByRow() {

    DataFrame df = DataFrameBuilder
            .builder("a", "b")
            .foldLongStreamByRow(-9999L, LongStream.of(-1, 1, 0, 2, 5, 3));
    new DataFrameAsserts(df, "a", "b").expectHeight(3)
            .expectLongColumns(0, 1)
            .expectRow(0, -1L, 1L)
            .expectRow(1, 0L, 2L)
            .expectRow(2, 5L, 3L);
}