@Test
    public void testIsConnected() {
        Mass other = new Mass(X, X);
        assertFalse(mass.isConnected(graph, other));

        graph.addMasses(mass);
        assertFalse(mass.isConnected(graph, other));

        graph.addMasses(other);
        assertFalse(mass.isConnected(graph, other));

        graph.addSpring(mass, other);
        assertTrue(mass.isConnected(graph, other));
    }