@Test
public void testMinimumlValue() {

    assertEquals(0, l1.minimumValue(network, LOAD), 0.);
    assertEquals(-100, l3.minimumValue(network), 0.);
    assertEquals(-100, l3.minimumValue(network, GENERATOR), 0.);
    assertEquals(20, l3.minimumValue(network, LOAD), 0.);
}