[Refactory] Clean UTs

tests/test_apis/test_single_gpu.py

tests/test_data/test_dataset.py

tests/test_data/test_dataset_builder.py

tests/test_data/test_loading.py

tests/test_data/test_transform.py

tests/test_data/test_tta.py

tests/test_eval_hook.py

tests/test_inference.py

tests/test_metrics.py

tests/test_models/test_heads/test_da_head.py

tests/test_models/test_heads/test_decode_head.py

tests/test_models/test_heads/test_enc_head.py

tests/test_models/test_heads/test_knet_head.py

tests/test_models/test_heads/test_point_head.py

tests/test_models/test_heads/test_stdc_head.py

tests/test_models/test_losses/__init__.py

tests/test_models/test_losses/test_ce_loss.py

tests/test_models/test_losses/test_dice_loss.py

tests/test_models/test_losses/test_focal_loss.py

tests/test_models/test_losses/test_lovasz_loss.py