public Set<String> getFailedPluginClassNames() {
    Collection<PluginUpgradeChecks> pluginUpgradeChecks = m_pluginChecks.values();

    return pluginUpgradeChecks.stream()
        .flatMap(plugins -> plugins.m_failedChecks.stream())
        .collect(Collectors.toSet());
  }
Gets all of the upgrade check classes defined in upgrade packs which were
not able to be loaded and instantiated.

@return all of the failed upgrade check classes.
ambari-server/src/main/java/org/apache/ambari/server/checks/UpgradeCheckRegistry.java