@Test
public void testFillValue() throws Exception {

    double[] expected = new double[]{
            NaN, 0.2, NaN, 0.4, 0.1, 0.2, NaN, 0.4,
            NaN, 0.3, NaN, NaN, 0.2, 0.3, 0.4, NaN,
            0.3, NaN, 0.1, 0.2, 0.3, 0.4, NaN, NaN,
            NaN, 0.1, 0.2, 0.3, 0.4, 0.1, NaN, NaN,
    };
    double[] actual = new double[expected.length];
    for (int i = 0; i < actual.length; i++) {
        actual[i] = arrayGrid.getSampleDouble(i % 8, i / 8);
    }
    assertArrayEquals(expected, actual, 1e-10);
}