New assertion `assertNotInHTML`, like `assertContains` has `assertNotContains`

[Thibaud Colas]

Django’s test assertions have assertContains and assertNotContains which are HTML-aware ways to check what’s inside a response, similar to Python’s assertIn and assertNotIn. Django also offers assertInHTML – but there is no assertNotInHTML.

This is very straightforward to implement – and I suspect more than a few projects will already have their own implementation if they need this, but I think it’d make much more sense to have this out of the box considering other "<needle> in <haystack>" assertions have their -not equivalent built in. For me, the main source of pain here is that I use this often enough to use this but rarely enough to frequently forget:

• Whether this is a Django built-in or not. So I look at ​assertions docs and am surprised not to see it.
• Whether the project I work on has it or not. So again I have to look around and potentially add it.

[Natalia Bidart]

I fully agree with the rationale, but for this, perhaps, Thibaud could you please create a forum post to allow for people to present any counter argument we may not be considering?

Thanks!

[Mariusz Felisiak]

I'm skeptic. Personally, I find the use of *NotIn* assertions really rare and not the best practice. There can many many reasons why something is not in something else, and it becomes even more unreliable when we do this in HTML. It's much more stable and bulletproof to use *In* assertions. I don't think it's worth adding.

Please first start a discussion on the DevelopersMailingList, where you'll reach a wider audience and see what other think, and ​follow the guidelines with regards to requesting features.

[Thibaud Colas]

Sorry about that, I thought I had read the ticket creation guidelines to check what the protocol is, but clearly missed the most important bits.

[Mariusz Felisiak]

Accepting based on the ​discussion.

Thibaud, would you like to prepare a patch?

[Thibaud Colas]

Yes please! Omg I might eventually become a code contributor.

[Lemuel Sta Ana]

Adding myself as CC, I'm very interested to see how the patch for this will be implemented. Hope you don't mind Thibaud.

[Nicolas Lupien]

PR ​https://github.com/django/django/pull/17626

[Mariusz Felisiak <felisiak.mariusz@…>]

In 2bf46c38:

Fixed #34658 -- Added SimpleTestCase.assertNotInHTML().