putEdge(N1, N2);

    assertThat(graphAsMutableGraph.putEdge(N2, N1)).isFalse();
  }

  /**
   * Tests that the method {@code putEdge} will silently add the missing nodes to the graph, then
   * add the edge connecting them. We are not using the proxy methods here as we want to test {@code
   * putEdge} when the end-points are not elements of the graph.
   */
  @Test

    putEdge(N1, N2);

    assertThat(graphAsMutableGraph.putEdge(N2, N1)).isFalse();
  }

  /**
   * Tests that the method {@code putEdge} will silently add the missing nodes to the graph, then
   * add the edge connecting them. We are not using the proxy methods here as we want to test {@code
   * putEdge} when the end-points are not elements of the graph.
   */
  @Test