docs: def start(self):
          """
          Try to remove the old mock logs first.
          """
          if self.resultdir:
              for lname in self.mock_logfiles:
                  self.logfiles[lname] = self.build.path_module.join(self.resultdir,
                                                                     lname)
          else:
              for lname in self.mock_logfiles:
                  self.logfiles[lname] = lname
          self.addLogObserver('state.log', MockStateObserver())
  
          cmd = remotecommand.RemoteCommand('rmdir', {'dir':
                                                      [self.build.path_module.join('build', self.logfiles[l])
                                                       for l in self.mock_logfiles]})
          d = self.runCommand(cmd)
          # must resolve super() outside of the callback context.
          super_ = super()
  
          @d.addCallback
          def removeDone(cmd):
              super_.start()
          d.addErrback(self.failed)