Create true tests for VCSs

[neerdoc]

The tests of the four supported VCSs are currently just checking that the call is made to the python subprocess. This is fragile and does not actually test that the calls are correct.

Create true test cases that actually sets up an empty repository of each VCS type and creates commits, adds, deletes, etc. to verify the code.

They will be more expensive in time and require that all four VCSs are installed, so that must also be added.