@Test
    public void testAddMassesOnMasses() {
        assertEquals(0, graph.masses.size());
        graph.addMasses(mass1, mass2, mass3);
        assertEquals(3, graph.masses.size());
        assertSame(mass1, graph.masses.get(0));
        assertSame(mass2, graph.masses.get(1));
        assertSame(mass3, graph.masses.get(2));
    }