test: update .gitlab-ci.yml for pytest

.gitlab-ci.yml

@@ -1,7 +1,21 @@
 stages:
-  - linting
+  - lint
+  - test
 
-lint:
+linting:
-  stage: linting
+  stage: lint
   script:
     - flake8
+
+building:
+  stage: test
+  script:
+    - python setup.py check -m -s
+    - python -m pip install -e .
+
+testing:
+  stage: test
+  script:
+    - python -m coverage run --branch --source mmcv -m pytest tests/
+    - python -m coverage xml
+    - python -m coverage report -m