@Test
public void testDifference() {

    IAtom carbon = mock(IAtom.class);
    IAtom oxygen = mock(IAtom.class);
    when(carbon.getSymbol()).thenReturn("C");
    when(oxygen.getSymbol()).thenReturn("O");
    IBond b1 = mock(IBond.class);
    IBond b2 = mock(IBond.class);
    when(b1.getOrder()).thenReturn(IBond.Order.SINGLE);
    when(b2.getOrder()).thenReturn(IBond.Order.DOUBLE);
    when(b1.getAtomCount()).thenReturn(2);
    when(b2.getAtomCount()).thenReturn(2);
    when(b1.getBegin()).thenReturn(carbon);
    when(b1.getEnd()).thenReturn(carbon);
    when(b2.getBegin()).thenReturn(carbon);
    when(b2.getEnd()).thenReturn(oxygen);
    IAtomContainer container1 = mock(IAtomContainer.class);
    IAtomContainer container2 = mock(IAtomContainer.class);
    when(container1.getElectronContainerCount()).thenReturn(1);
    when(container2.getElectronContainerCount()).thenReturn(1);
    when(container1.getElectronContainer(0)).thenReturn(b1);
    when(container2.getElectronContainer(0)).thenReturn(b2);
    String result = AtomContainerDiff.diff(container1, container2);
    Assert.assertNotNull(result);
}