Merge branch 'doc-use-aggregate-failures' into 'master'

Update rspec guidelines for aggregating failures

See merge request gitlab-org/gitlab!19512

doc/development/testing_guide/best_practices.md

@@ -61,6 +61,7 @@ bundle exec rspec spec/[path]/[to]/[spec].rb
 - When using `evaluate_script("$('.js-foo').testSomething()")` (or `execute_script`) which acts on a given element,
   use a Capyabara matcher beforehand (e.g. `find('.js-foo')`) to ensure the element actually exists.
 - Use `focus: true` to isolate parts of the specs you want to run.
+- Use [`:aggregate_failures`](https://relishapp.com/rspec/rspec-core/docs/expectation-framework-integration/aggregating-failures) when there is more than one expectation in a test.
 
 ### System / Feature tests