@Test public void testSize() {

    Graph g = new Graph(5);
    g.addAtom(mock(Atom.class));
    g.addAtom(mock(Atom.class));
    g.addAtom(mock(Atom.class));
    Edge e1 = new Edge(0, 1, Bond.IMPLICIT);
    Edge e2 = new Edge(0, 1, Bond.IMPLICIT);
    assertThat(g.size(), is(0));
    g.addEdge(e1);
    assertThat(g.size(), is(1));
    g.addEdge(e2);
    assertThat(g.size(), is(2));
}