Update documentation on writing tests for pylint

[DanielNoord]

• Add yourself to CONTRIBUTORS if you are a new contributor.
• Write a good description on what the PR does.

Type of Changes

	Type
✓	📜 Docs

Description

Thought I shouldn't ask for better documentation while not doing some of it myself. Nobody likes writing docs 😄

Based on my comment in #5365

[coveralls]

Pull Request Test Coverage Report for Build 1490882619

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 93.443%

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Totals
Change from base Build 1490184161:	0.0%
Covered Lines:	13923
Relevant Lines:	14900

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💛 - Coveralls

[DanielNoord]

Should probably add primer as well after we have merged it. I'll add it to the to-do list of the follow-up issue.

[Pierre-Sassoulas]

Amazing 👍 I have some small remarks

[Pierre-Sassoulas]

Suggested change

	For example, if the configuration should add a warning to the list of disabled messages the
	`.json` file should include::
	"functional_append": {
	"disable": [["a-message-to-be-added"],]
	}
	For example, if the configuration should add a warning to the list of disabled messages
	and you changed the configuration for ``job`` to 10 instead of the default 1 the
	`.json` file should include::
	"functional_append": {
	"disable": [["a-message-to-be-added"],]
	}
	"jobs": 10,

[DanielNoord]

👍

Can't commit this one as well..

[Pierre-Sassoulas]

Suggested change

	python -m tox -e py36 -- -k test_functional
	python -m tox -e py36 -- -k \*func\*
	python -m tox --recreate -e py36 -- -k test_functional # With recreation of the environment
	python -m tox -e py39 -- -k test_functional
	python -m tox -e py39 -- -k \*func\*
	python -m tox --recreate -e py39 -- -k test_functional # With recreation of the environment

Also upgraded the version so we appear hype :)

[DanielNoord]

Should we add those last 3 lines? The 5 lines after this basically cover pytest already.