def build_hooks()

in source/train.py [0:0]


    def build_hooks(self):
        """
        Extra hook to collect and plot evaluation metrics into TensorBoard. 
        """
        hooks = super().build_hooks()
        hooks.insert(-1, LossEvalHook(
            self.cfg.TEST.EVAL_PERIOD,
            self.model,
            build_detection_test_loader(
                self.cfg,
                self.cfg.DATASETS.TEST[0],
                DatasetMapper(self.cfg,True)
            )
        ))
        return hooks