private static final int EDGE_COUNT = 20;
  // TODO(user): Consider adding both error messages from here and {@link AbstractNetworkTest}
  // in one class (may be a utility class for error messages).
  private static final String ERROR_PARALLEL_EDGE = "connected by a different edge";
  private static final String ERROR_NEGATIVE_COUNT = "is non-negative";
  private static final String ERROR_ADDED_PARALLEL_EDGE =
      "Should not be allowed to add a parallel edge.";

    assertThat(e).hasMessageThat().contains(ERROR_PARALLEL_EDGE);
    e =
        assertThrows(
            IllegalArgumentException.class,
            () -> networkAsMutableNetwork.addEdge(N2, N1, EDGE_NOT_IN_GRAPH));
    assertThat(e).hasMessageThat().contains(ERROR_PARALLEL_EDGE);
  }

  @Test
  public void addEdge_parallelEdge_allowsParallelEdges() {

            IllegalArgumentException.class, () -> networkAsMutableNetwork.addEdge(N4, N5, E12));
    assertThat(e).hasMessageThat().contains(ERROR_REUSE_EDGE);
    e = assertThrows(IllegalArgumentException.class, () -> addEdge(N2, N1, E12));
    assertThat(e).hasMessageThat().contains(ERROR_REUSE_EDGE);
  }

  @Test
  public void addEdge_parallelEdge_notAllowed() {
    assume().that(graphIsMutable()).isTrue();

   * data, and vertical if there is variance in the {@code y} data but not the {@code x} data.
   *
   * <p>This fit minimizes the root-mean-square error in {@code y} as a function of {@code x}. This
   * error is defined as the square root of the mean of the squares of the differences between the
   * actual {@code y} values of the data and the values predicted by the fit for the {@code x}

        new Suppression(c1, tryException, c1Exception));
  }

  public void testErrors() throws IOException {
    Closer closer = new Closer(suppressor);

    Error c1Exception = new Error();
    Error c2Exception = new Error();
    Error c3Exception = new Error();

    TestCloseable c1 = closer.register(TestCloseable.throwsOnClose(c1Exception));
    TestCloseable c2 = closer.register(TestCloseable.throwsOnClose(c2Exception));

          } catch (Exception e) { // sneaky checked exception
            AssertionError error =
                new AssertionFailedError("Serialization failed on return value of " + factory);
            error.initCause(e.getCause());
            throw error;
          } catch (AssertionFailedError e) {
            AssertionError error =
                new AssertionFailedError(

  // identifiable substrings of expected error messages, from Strings that we've defined
  // here to provide error messages.
  // TODO(user): Some Strings used in the subclasses can be added as static Strings
  // here too.
  static final String ERROR_MODIFIABLE_SET = "Set returned is unexpectedly modifiable";
  static final String ERROR_SELF_LOOP = "self-loops are not allowed";

            Locale.ROOT,
            "Error in automated %s of %s\n"
                + "If the class is better tested explicitly, you can add %s() to %sTest",
            description,
            cls,
            explicitTestNames.get(0),
            cls.getName());
    AssertionFailedError error = new AssertionFailedError(message);
    error.initCause(e);
    return error;
  }

  /**

       * been cleared by this point.
       */
      reference.clear();
      try {
        ((FinalizableReference) reference).finalizeReferent();
      } catch (Throwable t) {
        logger.log(Level.SEVERE, "Error cleaning up after reference.", t);
      }
    }
  }

  /**
   * Iterates through the given loaders until it finds one that can load Finalizer.
   *
   * @return Finalizer.class
   */

       * been cleared by this point.
       */
      reference.clear();
      try {
        ((FinalizableReference) reference).finalizeReferent();
      } catch (Throwable t) {
        logger.log(Level.SEVERE, "Error cleaning up after reference.", t);
      }
    }
  }

  /**
   * Iterates through the given loaders until it finds one that can load Finalizer.
   *
   * @return Finalizer.class
   */