fix test tools bugs

tools/test.py

@@ -3,11 +3,11 @@ import argparse
 import torch
 import mmcv
 from mmcv.runner import load_checkpoint, parallel_test, obj_from_dict
-from mmcv.parallel import scatter, MMDataParallel
+from mmcv.parallel import scatter, collate, MMDataParallel
 
 from mmdet import datasets
 from mmdet.core import results2json, coco_eval
-from mmdet.datasets import collate, build_dataloader
+from mmdet.datasets import build_dataloader
 from mmdet.models import build_detector, detectors