@Test
public void testFoldDoubleStreamByRow() {

    DataFrame df = DataFrameBuilder
            .builder("a", "b")
            .foldDoubleStreamByRow(-9999.9, DoubleStream.of(-1, 1.1, 0, 2, 5, 3));
    new DataFrameAsserts(df, "a", "b")
            .expectHeight(3)
            .expectDoubleColumns(0, 1)
            .expectRow(0, -1., 1.1)
            .expectRow(1, 0., 2.)
            .expectRow(2, 5., 3.);
}