private IMockabilityResult collectNotMockableReasons(IMockCreationSettings settings) {
    return () -> makerList.stream()
      .map(m -> {
        IMockabilityResult result = isMockable(m, settings);
        if (!result.isMockable()) {
          return m.getId() + ": " + result.getNotMockableReason();
        }
        return null;
      })
      .filter(Objects::nonNull)
      .collect(Collectors.joining(NL));
  }
Returns {@code true} if the passed class is a Spock static mock currently active on the current {@link Thread}.

@param clazz the class to check
@return {@code true} if this class is a Spock static mock currently active on the current {@code Thread}
spock-core/src/main/java/org/spockframework/mock/runtime/MockMakerRegistry.java