@Override
  public void addOutEdge(E edge, N node) {
    super.addOutEdge(edge, node);
    Multiset<N> adjacentNodes = getReference(adjacentNodesReference);
    if (adjacentNodes != null) {
      checkState(adjacentNodes.add(node));
    }
  }

  private static <T> @Nullable T getReference(@Nullable Reference<T> reference) {
    return (reference == null) ? null : reference.get();
  }

        String expectedReference = "http://cwiki.apache.org/confluence/display/MAVEN/ConnectException";
        assertEquals(expectedReference, exceptionSummary.getReference());
    }

    @Test
    void testHandleExceptionAetherClassNotFound() {
        Throwable cause2 = new NoClassDefFoundError("org/sonatype/aether/RepositorySystem");
        Plugin plugin = new Plugin();

    }

    public Throwable getException() {
        return exception;
    }

    public String getMessage() {
        return message;
    }

    public String getReference() {
        return reference;
    }

    public List<ExceptionSummary> getChildren() {
        return children;
    }