I noticed the doc/development/testing_guide/best_practices.md still
referenced the `[run mysql]` tags, etc. They no longer work, so I
removed them, then realised I had better clean up the rest of
doc/development !

- Instead of Sidekiq::Testing.inline!, recommend the use of
perform_enqueued_jobs. This is due to the changes in
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20768

Signed-off-by: Rémy Coutable <remy@rymai.me>

In order for there to be a single source of truth.

Signed-off-by: Rémy Coutable <remy@rymai.me>

Signed-off-by: Takuya Noguchi <takninnovationresearch@gmail.com>

It mentions that explicitly defining dependencies in sources is
preferred over defining such dependencies only in spec files.

Adding the :prometheus tag to an rspec test will clear out
memory-mapped files and reset the registry.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/39968

Signed-off-by: Rémy Coutable <remy@rymai.me>

Signed-off-by: Rémy Coutable <remy@rymai.me>

Remove duplicate list item in "General Guidelines" Section.

I've followed the [upgrade guide](https://github.com/thoughtbot/factory_bot/blob/4-9-0-stable/UPGRADE_FROM_FACTORY_GIRL.md) and ran these two commands:

```
grep -e FactoryGirl **/*.rake **/*.rb -s -l | xargs sed -i "" "s|FactoryGirl|FactoryBot|"
grep -e factory_girl **/*.rake **/*.rb -s -l | xargs sed -i "" "s|factory_girl|factory_bot|"
```
Signed-off-by: Rémy Coutable <remy@rymai.me>

Signed-off-by: Rémy Coutable <remy@rymai.me>

Signed-off-by: Rémy Coutable <remy@rymai.me>

Tip from
https://robots.thoughtbot.com/write-reliable-asynchronous-integration-tests-with-capybara#directly-interacting-with-javascript

Tip from
https://robots.thoughtbot.com/write-reliable-asynchronous-integration-tests-with-capybara#directly-interacting-with-javascript

Signed-off-by: Rémy Coutable <remy@rymai.me>

Signed-off-by: Rémy Coutable <remy@rymai.me>