code: public static void fail(String failureMessage, Throwable realCause) {
      AssertionError error = Failures.instance().failure(failureMessage);
      error.initCause(realCause);
      throw error;
    }
docs: Throws an {@link AssertionError} with the given message and with the {@link Throwable} that caused the failure.
  
  @param failureMessage the description of the failed assertion. It can be {@code null}.
  @param realCause cause of the error.
  @throws AssertionError with the given message and with the {@link Throwable} that caused the failure.