@Test
public void testDiff() {

    IAtom carbon = mock(IAtom.class);
    IAtom oxygen = mock(IAtom.class);
    when(carbon.getSymbol()).thenReturn("C");
    when(oxygen.getSymbol()).thenReturn("O");
    ISingleElectron bond1 = mock(ISingleElectron.class);
    ISingleElectron bond2 = mock(ISingleElectron.class);
    when(bond1.getAtom()).thenReturn(carbon);
    when(bond2.getAtom()).thenReturn(oxygen);
    String result = SingleElectronDiff.diff(bond1, bond2);
    Assert.assertNotNull(result);
    Assert.assertNotSame(0, result.length());
    assertContains(result, "SingleElectronDiff");
    assertContains(result, "AtomDiff");
    assertContains(result, "C/O");
}