code: public static void failBecauseExceptionWasNotThrown(Class<? extends Throwable> throwableClass) {
      throw Failures.instance().failure(format("Expected %s to be thrown", throwableClass.getSimpleName()));
    }
docs: Throws an {@link AssertionError} with a message explaining that a {@link Throwable} of given class was expected to
  be thrown but had not been.
  
  @param throwableClass the Throwable class that was expected to be thrown.
  @throws AssertionError with a message explaining that a {@link Throwable} of given class was expected to be thrown
  but had not been.