Assist to add #[cfg(test)] to mod definition

[sbdchd]

My current workflow for adding a new test module is:

1. navigate to lib.rs
2. add mod foo_test; near the top

   mod foo_test;

3. add #[cfg(test)] above it

   #[cfg(test)]
   mod foo_test;

I think an assist option to add the #[cfg(test)] would be nice -- is it too specific?

[Veykril]

We have a completion snippet for this tmod (and then an assist that allows you to move an inline module mod foo {} into a mod foo; + create the corresponding file). An assist for this here sounds too niche/specific to me