docs: def wait_for(self, wait_for):
          """
          Wait for callback to return True.
  
          Simply returns if wait_for condition has been met,
          raises TimeoutExpired otherwise and kills the process.
  
          :param callback wait_for: callback to call
          :raises: mirakuru.exceptions.TimeoutExpired
          :returns: itself
          :rtype: SimpleExecutor
          """
          while self.check_timeout():
              if wait_for():
                  return self
              time.sleep(self._sleep)
  
          self.kill()
          raise TimeoutExpired(self, timeout=self._timeout)