@Test(expected = IllegalStateException.class)
public void testAddABeforeB() {

	String e = "e";
	this.set.addABeforeB(A, e);
	this.set.addABeforeB(e, B);
	assertTrue("Since a before e was added, this should also be allowed.", this.set.allowsABeforeB(A, e));
	assertTrue("Since e before b was added, this should also be allowed.", this.set.allowsABeforeB(e, B));
	assertTrue("Since e before b was added, this should also be allowed.", this.set.allowsABeforeB(e, C));
	assertTrue("Since e before b was added, this should also be allowed.", this.set.allowsABeforeB(e, D));
	// negative test, because by transitivity this shouldn't be allowed.
	this.set.addABeforeB(C, e);
}