@Test(expected = IllegalArgumentException.class)
public void unplacedNonHydrogen() {

    HydrogenPlacer hydrogenPlacer = new HydrogenPlacer();
    // c2 is unplaced
    IAtom c1 = new Atom("C", new Point2d(0, 0));
    IAtom c2 = new Atom("C");
    IAtomContainer m = new AtomContainer();
    m.addAtom(c1);
    m.addAtom(c2);
    m.addBond(new Bond(c1, c2));
    hydrogenPlacer.placeHydrogens2D(m, 1.5);
}