}

  // Node sets are the same, but edge sets differ.
  @Test
  public void equivalent_edgeSetsDiffer() {
    network.addEdge(N1, N2, E12);

    MutableNetwork<Integer, String> g2 = createNetwork(edgeType);
    g2.addEdge(N1, N2, E13);

    assertThat(network).isNotEqualTo(g2);
  }

  // Node/edge sets are the same, but node/edge connections differ due to edge type.
  @Test

/**
 * An immutable pair representing the two endpoints of an edge in a graph. The {@link EndpointPair}
 * of a directed edge is an ordered pair of nodes ({@link #source()} and {@link #target()}). The
 * {@link EndpointPair} of an undirected edge is an unordered pair of nodes ({@link #nodeU()} and
 * {@link #nodeV()}).
 *
 * <p>The edge is a self-loop if, and only if, the two endpoints are equal.
 *
 * @author James Sexton

                </mxCell>
                <mxCell id="8" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeWidth=3;exitX=0.092;exitY=1.01;exitDx=0;exitDy=0;dashed=1;exitPerimeter=0;" parent="1" edge="1">
                    <mxGeometry relative="1" as="geometry">
                        <Array as="points">
                            <mxPoint x="800" y="521"/>
                            <mxPoint x="800" y="560"/>

                </mxCell>
                <mxCell id="8" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeWidth=3;exitX=0.092;exitY=1.01;exitDx=0;exitDy=0;dashed=1;exitPerimeter=0;" parent="1" edge="1">
                    <mxGeometry relative="1" as="geometry">
                        <Array as="points">
                            <mxPoint x="800" y="521"/>
                            <mxPoint x="800" y="560"/>

            List<String> cycle = visitCycle(graph, Collections.singleton(to), new HashMap<>(), new LinkedList<>());
            if (cycle != null) {
                // remove edge which introduced cycle
                throw new CycleDetectedException(
                        "Edge between '" + from + "' and '" + to + "' introduces to cycle in the graph", cycle);
            }
        }
    }

    private enum DfsState {
        VISITING,

                    <mxGeometry relative="1" as="geometry"/>
                </mxCell>
                <mxCell id="20" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;endArrow=none;endFill=0;strokeWidth=3;" parent="1" source="11" target="18" edge="1">
                    <mxGeometry relative="1" as="geometry"/>

                </mxCell>
                <mxCell id="8" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeWidth=3;exitX=0.092;exitY=1.01;exitDx=0;exitDy=0;dashed=1;exitPerimeter=0;" parent="1" edge="1">
                    <mxGeometry relative="1" as="geometry">
                        <Array as="points">
                            <mxPoint x="800" y="521"/>
                            <mxPoint x="800" y="560"/>

                </mxCell>
                <mxCell id="8" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeWidth=3;exitX=0.092;exitY=1.01;exitDx=0;exitDy=0;dashed=1;exitPerimeter=0;" parent="1" edge="1">
                    <mxGeometry relative="1" as="geometry">
                        <Array as="points">
                            <mxPoint x="800" y="521"/>
                            <mxPoint x="800" y="560"/>

                </mxCell>
                <mxCell id="8" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeWidth=3;exitX=0.092;exitY=1.01;exitDx=0;exitDy=0;dashed=1;exitPerimeter=0;" parent="1" edge="1">
                    <mxGeometry relative="1" as="geometry">
                        <Array as="points">
                            <mxPoint x="800" y="521"/>
                            <mxPoint x="800" y="560"/>

                </mxCell>
                <mxCell id="8" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeWidth=3;exitX=0.092;exitY=1.01;exitDx=0;exitDy=0;dashed=1;exitPerimeter=0;" parent="1" edge="1">
                    <mxGeometry relative="1" as="geometry">
                        <Array as="points">
                            <mxPoint x="800" y="521"/>
                            <mxPoint x="800" y="560"/>