Found an issue when `@slow` isn't the last decorator (gets ignored!), so documenting this significance.
* [docs] add testing documentation * Update docs/source/testing.rst Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com> * tweaks as suggested * Update docs/source/testing.rst Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com> * Update docs/source/testing.rst Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com> * Update docs/source/testing.rst Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com> * Update docs/source/testing.rst Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com> * Update docs/source/testing.rst Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com> * Update docs/source/testing.rst Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com> * Update docs/source/testing.rst Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com> * Update docs/source/testing.rst Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com> * Update docs/source/testing.rst Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com> * Update docs/source/testing.rst Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com> * Update docs/source/testing.rst Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com> * tweaks * Update docs/source/testing.rst Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com> * Update docs/source/testing.rst Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com> * more tweaks * suggestions from @LysandreJik Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>