Test: Git as an SCM extension

[joaomoreno]

Test for #18615, #15246
Complexity 4

• Windows - @ramya-rao-a
• OS X - @sandy081
• Linux - @roblourens

Test Steps

There has been an exploration towards having SCM providers in VS Code. Git is halfway implemented on top of it. In order to test it, you must run the SCM: Enable Preview SCM global command.

Before filing for missing features, refer to #18615, where most of those are tracked.

• Test that the SCM: Enable Preview SCM and SCM: Disable Preview SCM work as advertised: they should toggle between having the classic git UI to having the new SCM viewlet
• Test that when Preview SCM is disabled, git works just as before
• With Preview SCM enabled:
  • Test that the viewlet's contents always match what git status would show
  • Test the diff editor which opens upon click of the viewlet's items
  • Test that there are still dirty diff decorations in the gutter margin of the editor
  • Test staging, undoing and unstaging commands/actions
  • Test commit command
  • Test sync, pull, push & publish commands
  • Test that merge conflict decorations appear highlighted
  • Test that you can checkout branches using the status bar & global command
  • Test that you can create branches using the global command
  • Test the viewlet menu actions as well as context actions
  • Test that the git output channel's content makes sense
  • Test that there's a git fetch every now and then (check the git output)