Set<Address> getEdgeSources(EdgeDef edge) {
        return sources.get(edge.edgeId());
    }
@Test
    public void when_traversingDATAAndCheckExistenceOfConnectionTo() {
        VertexDef vertex_1 = createMockVertex(1);
        VertexDef vertex_2 = createMockVertex(2);
        List<VertexDef> vertices = Arrays.asList(vertex_1, vertex_2);
        EdgeDef edge_1_2 = createEdge(vertex_1, vertex_2, null);

        DagNodeUtil util = new DagNodeUtil(vertices, allAddresses, node1Address);
        assertTrue(util.getEdgeSources(edge_1_2).contains(node1Address));
    }