code: def set(self, value: Optional[bool]):
          
          prev_value = self._value
          self._value = value
          if self._value != prev_value:
              # notify all watchers that this check was changed
              for event in self._events:
                  event.set()
docs: Sets current status of a check
  
          :param value: ``True`` (healthy), ``False`` (unhealthy), or ``None``
              (unknown)