I thought of implementing an assertNotRaises to solve the issue of using try...except...fail in order to prevent showing the tests as an error and instead show them as a failure.
Is there anything I should consider while implementing it?

Yes. What does such an assertion actually mean?

Why would I write `self.assertNotRaises(ValueError, spam, arg)` rather than just call `spam(arg)`? The only difference is that assertNotRaises will treat one specific exception as a test failure rather than a error, but I don't think that's useful. spam(arg) presumably is supposed to return something, or do something, not merely "don't raise ValueError". Raising ValueError should be no different from raising any other exception: it's a error, not a failure.

It makes sense to test for expected exceptions. I don't think it makes sense to test for exceptions that don't happen. Every single successful test of `spam(arg)` shows that ValueError is not raised, as well as every imaginable other exception. I don't think there is any need for an assert method to test for exceptions not being raised.

Agreed.  I've never used the distinction between errors and failures myself.

I concur with David snd Steven, so closing this as rejected.