code: static Class<? extends Standalone> resolveStandaloneClass(String standaloneClassNameSystemProperty,
                                                                ForwardingServiceLoader<Standalone> standaloneServiceLoader,
                                                                String standaloneClassNameDefaultValue) {
          Class<? extends Standalone> resolvedStandaloneClass = null;
          
          // 1. System property for 'ninja.standalone.class'
          if (standaloneClassNameSystemProperty != null) {
              try {
                  resolvedStandaloneClass
                      = (Class<Standalone>)Class.forName(standaloneClassNameSystemProperty);
              } catch (Exception e) {
                  throw new RuntimeException("Unable to find standalone class '" + standaloneClassNameSystemProperty + "' (class does not exist)");
              }
          }
          
          // 2. Implementation on classpath that's registered as service?
          if (resolvedStandaloneClass == null) {
              try {
                  Iterator<Standalone> standaloneIterator = standaloneServiceLoader.iterator();
                  // first one wins
                  if (standaloneIterator.hasNext()) {
                      resolvedStandaloneClass = standaloneIterator.next().getClass();
                  }
                  // more than one triggers warning
                  if (standaloneIterator.hasNext()) {
                      log.warn("More than one implementation of {} on classpath! Using {} which was the first", Standalone.class, resolvedStandaloneClass);
                  }
              } finally {
                  // always kill cache (since ServiceLoader actually instantiates an instance)
                  standaloneServiceLoader.reload();
              }
          }
          
          // 3. Fallback to ninja default
          if (resolvedStandaloneClass == null) {
              try {
                  resolvedStandaloneClass
                      = (Class<Standalone>)Class.forName(standaloneClassNameDefaultValue);
              } catch (Exception e) {
                  throw new RuntimeException("Unable to find standalone class '" + standaloneClassNameDefaultValue + "' (class does not exist)");
              }
          }
          
          return resolvedStandaloneClass;
      }
docs: used for testing (so we can inject mocks of system static methods)