addEdge(N1, N1, E11);
    assertThat(network.successors(N1)).containsExactly(N1);
    addEdge(N2, N1, E12);
    assertThat(network.successors(N1)).containsExactly(N1, N2);
  }

  @Test
  public void degree_selfLoop() {
    assume().that(network.allowsSelfLoops()).isTrue();

    addEdge(N1, N1, E11);
    assertThat(network.degree(N1)).isEqualTo(2);
    addEdge(N1, N2, E12);
    assertThat(network.degree(N1)).isEqualTo(3);

    putEdge(N1, N2);
    assertThat(graph.predecessors(N1)).containsExactly(N1, N2);
  }

  @Test
  public void successors_selfLoop() {
    assume().that(graph.allowsSelfLoops()).isTrue();

    putEdge(N1, N1);
    assertThat(graph.successors(N1)).containsExactly(N1);
    putEdge(N2, N1);
    assertThat(graph.successors(N1)).containsExactly(N1, N2);
  }

  @Test
  public void incidentEdges_selfLoop() {

    }
  }

  /** Returns the product of {@code n1} exclusive through {@code n2} inclusive. */
  @SuppressWarnings("UseCorrectAssertInTests") // TODO(b/345814817): Remove or convert assertion.
  private static BigInteger oldSlowFactorial(int n1, int n2) {
    assert n1 <= n2;
    if (IntMath.log2(n2, CEILING) * (n2 - n1) < Long.SIZE - 1) {
      // the result will definitely fit into a long
      long result = 1;

    g1.putEdge(N1, N2);
    g1.putEdge(N3, N1);

    // for g2, add 3->1 first, then 1->2
    g2.putEdge(N3, N1);
    g2.putEdge(N1, N2);

    assertThat(g1).isEqualTo(g2);
  }

  @Test
  public void equivalent_edgeDirectionsDiffer() {
    graph.putEdge(N1, N2);

    MutableGraph<Integer> g2 = createGraph(edgeType);
    g2.putEdge(N2, N1);

    switch (edgeType) {

    g1.putEdge(N1, N2);
    g1.putEdge(N3, N1);

    // for g2, add 3->1 first, then 1->2
    g2.putEdge(N3, N1);
    g2.putEdge(N1, N2);

    assertThat(g1).isEqualTo(g2);
  }

  @Test
  public void equivalent_edgeDirectionsDiffer() {
    graph.putEdge(N1, N2);

    MutableGraph<Integer> g2 = createGraph(edgeType);
    g2.putEdge(N2, N1);

    switch (edgeType) {

    addEdge(N1, N1, E11);
    assertThat(network.degree(N1)).isEqualTo(2);
    addEdge(N1, N2, E12);
    assertThat(network.degree(N1)).isEqualTo(3);
  }

  @Test
  public void inDegree_selfLoop() {
    assume().that(network.allowsSelfLoops()).isTrue();

    addEdge(N1, N1, E11);
    assertThat(network.inDegree(N1)).isEqualTo(1);
    addEdge(N4, N1, E41);
    assertThat(network.inDegree(N1)).isEqualTo(2);
  }

    addEdge(N1, N1, E11);
    assertThat(network.degree(N1)).isEqualTo(2);
    addEdge(N1, N2, E12);
    assertThat(network.degree(N1)).isEqualTo(3);
  }

  @Test
  public void inDegree_selfLoop() {
    assume().that(network.allowsSelfLoops()).isTrue();

    addEdge(N1, N1, E11);
    assertThat(network.inDegree(N1)).isEqualTo(1);
    addEdge(N4, N1, E41);
    assertThat(network.inDegree(N1)).isEqualTo(2);
  }

    putEdge(N1, N2);
    assertThat(graph.predecessors(N1)).containsExactly(N1, N2);
  }

  @Test
  public void successors_selfLoop() {
    assume().that(graph.allowsSelfLoops()).isTrue();

    putEdge(N1, N1);
    assertThat(graph.successors(N1)).containsExactly(N1);
    putEdge(N2, N1);
    assertThat(graph.successors(N1)).containsExactly(N1, N2);
  }

  @Test
  public void incidentEdges_selfLoop() {

	}

	return relTag, t
}

// commitID returns the abbreviated commit-id hash of the last commit.
func commitID() string {
	// git log --format="%H" -n1
	var (
		commit []byte
		err    error
	)
	cmdName := "git"
	cmdArgs := []string{"log", "--format=%H", "-n1"}
	if commit, err = exec.Command(cmdName, cmdArgs...).Output(); err != nil {
		fmt.Fprintln(os.Stderr, "Error generating git commit-id: ", err)
		os.Exit(1)
	}

    addEdge(N1, N1, E11);
    addEdge(N1, N1, E11_A);
    addEdge(N1, N2, E12);
    assertTrue(networkAsMutableNetwork.removeEdge(E11_A));
    assertThat(network.edgesConnecting(N1, N1)).containsExactly(E11);
    assertThat(network.edgesConnecting(N1, N2)).containsExactly(E12);
    assertTrue(networkAsMutableNetwork.removeEdge(E11));
    assertThat(network.edgesConnecting(N1, N1)).isEmpty();