id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
34657	Testing assertions `assertContains` and `assertInHTML` should output the haystack on failure	Thibaud Colas	Chinmoy	"If I use the vanilal Python `assertIn` or `assertRegex`, when the assertion fails, it’s very simple to assess what went wrong from the test error only:

{{{
    self.assertIn(""<b>hey</b>"", ""<p>Howdy!</p>"")
AssertionError: '<b>hey</b>' not found in '<p>Howdy!</p>'
}}}

With Django’s `assertContains` and `assertInHTML`, this gets much harder:

{{{
    self.assertInHTML(""<b>hey</b>"", ""<p>Howdy!</p>"")
  File ""/Users/thibaudcolas/Dev/django/html-testing-with-django/.venv/lib/python3.11/site-packages/django/test/testcases.py"", line 1076, in assertInHTML
    self.assertTrue(
AssertionError: False is not true : Couldn't find '<b>
hey
</b>' in response
}}}

and:

{{{
    self.assertContains(res, ""<b>hey</b>"")
  File ""/Users/thibaudcolas/Dev/django/html-testing-with-django/.venv/lib/python3.11/site-packages/django/test/testcases.py"", line 660, in assertContains
    self.assertTrue(
AssertionError: False is not true : Couldn't find '<b>hey</b>' in response
}}}

--- 

In both cases, Django doesn’t display the haystack – so I have to waste a lot of time going back to my HTML templates to check what they might be outputting / or potentially load the same scenario in a browser / or manually add `print` statements to my test cases. This is all very time-consuming. Instead, it’d be much better if the haystack was just present.

Additionally for `assertInHTML` – it’s annoying that `needle` as displayed in the failure message is the parser’s output, which is therefore broken up over multiple lines. It’d be much nicer if the example above resulted in `AssertionError: False is not true : Couldn't find '<b>hey</b>' in response`.

---

Test suite I used to compare output for reference: https://github.com/thibaudcolas/html-testing-with-django/blob/39c82c410cce4bea71ac54be27be67057f4d8dd8/testing_tests/tests.py#L5

And link to Python’s `assertIn` / `assertNotIn` implementations: https://github.com/python/cpython/blob/101d5ec7d7fe122fa81a377c8ab8b562d1add9ee/Lib/unittest/case.py#L1147-L1159"	New feature	closed	Testing framework	dev	Normal	fixed	HTML, assertions, testing	Chinmoy	Ready for checkin	1	0	0	0	0	0