docs(tests): add guide for generating coverage reports

apps/notification/tests/README.md

@@ -0,0 +1,32 @@
+## unittest
+```shell
+# run the command
+
+cd test/unit_test
+python -m pytest unit_test_file.py -v --cov=backend.tested_directory --cov-report=html
+```
+After the test is completed, a htmlcov folder will be generated. The test result is in the htmlcov/index.html.
+
+## integration test
+```shell
+# run the command
+
+cd test/integration_test
+python -m pytest integration_test_file.py -v -s --html=report.html --self-contained-html --asyncio-mode=auto
+
+```
+After the test is completed, a report.html will be generated. The test result is in the file.
+```shell
+python integration_test_file.py 
+python -m coverage html --include="../../backend/tested_directory/*"
+```
+After the test is completed, a htmlcov folder will be generated. The test result is in the htmlcov/index.html.
+
+
+## Q & A
+### Q: ModuleNotFoundError: No module named 'backend'
+```shell
+# export freeleaps code path
+
+export PYTHONPATH="/yourpath/freeleaps-service-hub/apps/notification"
+```