add testing note

Author: t-bltg

docs/src/contributing.md

@@ -186,7 +186,7 @@ Many people have trouble with Git.  More have trouble with Github.  I think much
 Here are some guidelines for the development workflow (Note: Even if you've made 20 PRs to Plots in the past, please read this as it may be different than past guidelines):
 
 - **Commit to a branch that belongs to you.**  Typically that means you should give your branches names that are unique to you, and that might include information on the feature you're developing.  For example, I might choose to `git checkout -b tb-fonts` when starting work on fonts.
-- **Open a PR against master.**  `master` is the "bleeding edge".  (Note: I used to recommend `PR`ing to `dev`)
+- **Open a PR against the development branch (can be `master` or `v2`), where `v2` is the "bleeding edge".
 - **Only merge others changes when absolutely necessary.** You should prefer to use `git rebase origin/master` instead of `git merge origin/master`.  A rebase replays your recent commits on top of the most recent `master`, avoiding complicated and messy merge commits and generally avoiding confusion.  If you follow the first rule, then you likely won't get yourself in trouble.  Rebase horror stories generally result when many people are working on the same branch.  I find [this resource](https://git-scm.com/book/en/v2/Git-Branching-Rebasing) is great for understanding the important parts of `git rebase`.
 
 ---
@@ -243,7 +243,7 @@ Power up your favorite editor (maybe [Juno](https://junolab.org/)?) and make som
 
 Format your changes (code style consistency) using:
 ```bash
-$ julia -e 'using Runic; exit(Runic.main(ARGS))'
+$ julia -e 'using Runic; exit(Runic.main(ARGS))' -- --inplace .
 ```
 
 #### Commit
@@ -291,6 +291,18 @@ The version number (vMAJOR.MINOR.PATCH) should be incremented using [semver](htt
 
 ### Testing
 
+Testing individual `Plots` components suche as `PlotsBase` is as simple as :
+```bash
+$ cd Plots.jl/PlotsBase
+$ julia --project=. -e 'using Pkg; Pkg.test()'
+```
+
+, or for `RecipesBase` :
+```bash
+$ cd Plots.jl
+$ julia --project=RecipesBase -e 'using Pkg; Pkg.test()'
+```
+
 #### VisualRegressionTests
 
 Testing in Plots is done with the help of [VisualRegressionTests](https://github.com/JuliaPlots/VisualRegressionTests.jl).  Reference images are stored in [PlotReferenceImages](https://github.com/JuliaPlots/PlotReferenceImages.jl). Sometimes the reference images need to be updated (if features change, or if the underlying backend changes).  VisualRegressionTests makes it somewhat painless to update the reference images: