keras/src/callbacks/tensorboard.py/TensorBoard/on_test_end
class TensorBoard:    def on_test_end(self, logs=None):
        if self.model.optimizer and hasattr(self.model.optimizer, "iterations"):
            with self._val_writer.as_default():
                for name, value in logs.items():
                    self.summary.scalar(
                        "evaluation_" + name + "_vs_iterations",
                        value,
                        step=self.model.optimizer.iterations,
                    )
        self._pop_writer()