if (logger.isDebugEnabled()) {
                    logger.debug("container was destroyed.");
                }
                return;
            }
            logger.warn("Failed to store a failure url.", e);
        }

        if (cae.isDebugEnabled()) {
            logger.debug("[{}] Crawling Access Exception at {}", failureUrlId, urlQueue.getUrl(), cae);
        } else if (cae.isInfoEnabled()) {

- plugin artifact retrieval problem
- plugin dependency metadata missing
- plugin dependency metadata retrieval problem
- plugin configuration problem
- plugin execution failure due to something that is know to possibly go wrong (like compilation failure)
- plugin execution error due to something that is not expected to go wrong (the compiler executable missing)

          },
          "route": {
           "cluster": "outbound|8000||httpbin.default.svc.cluster.local",
           "timeout": "0s",
           "retry_policy": {
            "retry_on": "connect-failure,refused-stream,unavailable,cancelled,retriable-status-codes",
            "num_retries": 2,
            "retry_host_predicate": [
             {
              "name": "envoy.retry_host_predicates.previous_hosts",

   * the call to {@code contains(null)} is permitted to throw a {@code NullPointerException}.
   *
   * @param message message to use upon assertion failure
   */
  protected void expectNullKeyMissingWhenNullKeysUnsupported(String message) {
    try {
      assertFalse(message, getMap().containsKey(null));
    } catch (NullPointerException tolerated) {

        wagonManager.getArtifact(artifact, repo, null, false);

        wagon.clearExpectedContent();
        wagon.addExpectedContent("path", "expected-failure");
        wagon.addExpectedContent("path.sha1", "b7bb97d7d0b9244398d9b47296907f73313663e6");
        assertThrows(
                ChecksumFailedException.class,

    while (queue.isNotEmpty()) {
        val dependency = when (val result = queue.removeFirst()) {
            is ResolvedDependencyResult -> result
            is UnresolvedDependencyResult -> throw result.failure
            else -> throw AssertionError("Unknown dependency type: $result")
        }

        if (dependency.isConstraint) {
            continue
        }

        val to = dependency.resolvedVariant

//   and therefore is passed around as a pointer to an opaque
//   struct as mentioned above.
// * Every call that has a TF_Status* argument clears it on success
//   and fills it with error info on failure.
// * unsigned char is used for booleans (instead of the 'bool' type).
//   In C++ bool is a keyword while in C99 bool is a macro defined
//   in stdbool.h. It is possible for the two to be inconsistent.

        withEnv(["JAVA_HOME=${ tool "JDK 1.8 (latest)" }", "PATH+MAVEN=${tool 'Maven 3.6.3'}/bin:${env.JAVA_HOME}/bin"]) {
          sh "mvn clean install -V -B -Prun-its,embedded -Dmaven.test.failure.ignore -Dmaven.repo.local=${env.WORKSPACE}/repo -DmavenDistro=${env.WORKSPACE}/apache-maven/target/apache-maven-bin.zip"
        }
      }
    }
  }
  post {
    always {

    val call = client.newCall(Request(url))
    val response = call.execute()
    assertThat(response.body.string()).isEqualTo("hello from IPv6")

    // In the process we made two connection attempts including one failure.
    assertThat(listener.recordedEventTypes().filter { it == "ConnectStart" }).hasSize(1)
    assertThat(listener.recordedEventTypes().filter { it == "ConnectEnd" }).hasSize(1)

      }
    }
  };

  ...
}
```

### Events with Failures

When an operation fails, a failure method is called. This is `connectFailed()` for failures while building a connection to the server, and `callFailed()` when the HTTP call fails permanently. When a failure happens it is possible that a `start` event won’t have a corresponding `end` event.

![Events Diagram](../assets/images/******@****.***)