private void initializeConfigurations(List<Class<?>> initialConfigurations) {
    for (Class<?> configuration : initialConfigurations) {
      ConfigurationObject annotation = configuration.getAnnotation(ConfigurationObject.class);
      if (annotation == null) {
        throw new InternalSpockError("Not a @ConfigurationObject: %s").withArgs(configuration);
      }
      createAndStoreConfiguration(configuration, annotation);
    }
  }
Maintains a registry of global Spock extensions and their configuration objects,
which can be used to configure other extensions.

@author Peter Niederwieser
spock-core/src/main/java/org/spockframework/runtime/GlobalExtensionRegistry.java