* Verifies that the {@code Set} returned by {@code adjacentEdges} has the expected mutability
   * property (see the {@code Network} documentation for more information).
   */
  @Test
  public abstract void adjacentEdges_checkReturnedSetMutability();

  /**
   * Verifies that the {@code Set} returned by {@code edgesConnecting} has the expected mutability
   * property (see the {@code Network} documentation for more information).
   */
  @Test