@Test(expectedExceptions = IllegalArgumentException.class)
public void testAddUndirectedExistingDirected() {

    EdgeImpl directed = GraphGenerator.generateSingleEdge();
    EdgeStore edgeStore = new EdgeStore();
    edgeStore.add(directed);
    EdgeImpl undirectedSameOrder = new EdgeImpl("4", directed.source, directed.target, directed.type, 1.0, false);
    Assert.assertFalse(edgeStore.add(undirectedSameOrder));
    EdgeImpl undirectedOtherOrder = new EdgeImpl('5', directed.target, directed.source, directed.type, 1.0, false);
    edgeStore.add(undirectedOtherOrder);
}