code: public void notThrown(Class<? extends Throwable> type) {
      Throwable thrown = getSpecificationContext().getThrownException();
      if (thrown == null) return;
      if (type.isAssignableFrom(thrown.getClass())) {
        throw new UnallowedExceptionThrownError(type, thrown);
      }
      ExceptionUtil.sneakyThrow(thrown);
    }
docs: Specifies that no exception of the given type should be
  thrown, failing with a {@link UnallowedExceptionThrownError} otherwise.
  
  @param type the exception type that should not be thrown