@Test public void atoms() {

    Graph g = new Graph(20);
    g.addAtom(mock(Atom.class));
    g.addAtom(mock(Atom.class));
    g.addAtom(mock(Atom.class));
    g.addAtom(mock(Atom.class));
    Iterable<Atom> atoms = g.atoms();
    Iterator<Atom> it    = atoms.iterator();
    assertTrue(it.hasNext());
    assertNotNull(it.next());
    assertTrue(it.hasNext());
    assertNotNull(it.next());
    assertTrue(it.hasNext());
    assertNotNull(it.next());
    assertTrue(it.hasNext());
    assertNotNull(it.next());
    assertFalse(it.hasNext());
}