code: def which(cwd=None):  # pragma: no cover
          
          if cwd is None:
              cwd = os.getcwd()
          for (k, using_vc) in globals().items():
              if k.startswith('using_') and using_vc(cwd=cwd):
                  return VersionControl.from_string(k[6:])
  
          # Not supported (yet)
          raise NotImplementedError("Unknown version control system, "
                                    "or you're not in the project directory.")
docs: Try to find which version control system contains the cwd directory.
  
          Returns the VersionControl superclass e.g. Git, if none were
          found this will raise a NotImplementedError.