@Test
public void testDiff() {

    IAtom atom1 = mock(IAtom.class);
    IAtom atom2 = mock(IAtom.class);
    when(atom1.getSymbol()).thenReturn("H");
    when(atom2.getSymbol()).thenReturn("C");
    String result = AtomDiff.diff(atom1, atom2);
    Assert.assertNotNull(result);
    Assert.assertNotSame(0, result.length());
    assertContains(result, "AtomDiff");
    assertContains(result, "H/C");
}