@Test
public void testSumReducer() {

    Double[][] testLists = new Double[][] {
            {},
            {null, null},
            {1.0, null},
            {1.0, 2.1}
    };
    Double[] results = new Double[] {
            0.0,
            0.0,
            1.0,
            3.1
    };
    for (int i = 0; i < results.length; i++) {
        Double[] test = testLists[i];
        Double expResult = results[i];
        Double result = Reducers.sumReducer(Arrays.asList(test));
        Assert.assertEquals(expResult, result);
    }
}