Add tests for global command

[voxsim]

This pull request adds:

• tests for every global command excluding upgradeInteractive and everyone is side-effect free (I hope)
• move the pre-existent tests under isCI branch because they cause some changes in the prefix or global folder; but If I am wrong please let me know O.o
• Fix Global packages unavailable #3162, yarn global ls does not list global packages #3142, Problems installing packages globally #3089 (?)
• It closes Fix user home config conflicting with the test suite #2725 ;)

cc @bestander @arcanis

[voxsim]

IMO we should remove reporter and install from checkInstalled function because they were never used. I will try to open another pull-request to see if I am right O.o

[voxsim]

@bestander if you don't have time to review this PR right now, I can open a mini PR that fixes for #3142. yarn global ls does not work because we pass the flag skipIntegrity instead of skipIntegrityCheck.

[arcanis]

@voxsim There's a test that fails on Windows, can you give it a look?

 FAIL  __tests__\commands\global.js (16.563s)
  ● bin
    Error: expect(string).toContain(value)
    
    Expected string:
      "C:\\Users\\appveyor\\AppData\\Local\\Temp\\1\\yarn-global-0.40320568132368995
    "
    To contain value:
      "C:\\Users\\appveyor\\AppData\\Local\\Temp\\1\\yarn-global-0.40320568132368995\\bin"
      
      at runGlobal (__tests__\commands\global.js:80:25)
      at __tests__\commands\_helpers.js:135:15
      at next (native)
      at step (node_modules\babel-runtime\helpers\asyncToGenerator.js:17:30)
      at node_modules\babel-runtime\helpers\asyncToGenerator.js:28:13
      Console output:
       C:\Users\appveyor\AppData\Local\Temp\1\yarn-global-0.40320568132368995
      
      at __tests__\commands\_helpers.js:138:13
      at next (native)
      at step (node_modules\babel-runtime\helpers\asyncToGenerator.js:17:30)
      at node_modules\babel-runtime\helpers\asyncToGenerator.js:28:13

[TimvdLippe]

I assume this also closes #2725?

[voxsim]

@arcanis ok I will look this tomorrow ;)

@TimvdLippe yes it should close that pull request, but please check it, ok?

[TimvdLippe]

@voxsim Sure, will do tomorrow 😄

[voxsim]

@arcanis now should work ;)

[TimvdLippe]

Can confirm it actually runs on my machine now, finally a green build! Not sure if isCI is the nicest solution, but at least it works for now. Could you add Closes #2725 to the pull request description?

[voxsim]

@TimvdLippe done ;)

[voxsim]

@TimvdLippe I didn't delete that tests because I have no idea how to prove that tests are useful or not. For what I understand we can delete without worries.

[arcanis]

That's great, thanks! Let's merge it! :)