@Test
public void testDifference() {

    IAtomType element1 = mock(IAtomType.class);
    IAtomType element2 = mock(IAtomType.class);
    when(element1.getHybridization()).thenReturn(PLANAR3);
    when(element2.getHybridization()).thenReturn(SP3);
    IDifference difference = AtomTypeDiff.difference(element1, element2);
    Assert.assertNotNull(difference);
}