add testing doc

docs/Testing.md

@@ -0,0 +1,17 @@
+# Testing
+
+To run the end-to-end tests the OpenAPI Python client should be generated first:
+```
+openapi-generator generate -i ./api.yml -g python --package-name nomilo_client -o ./python_client
+```
+
+Then install, here a virtual env is created for this purpose:
+```
+python -m venv env
+env/bin/pip install ./python_client
+```
+
+You are now all set to run the e2e tests, note that Nomilo must be started first:
+```
+env/bin/python -m unittest e2e/*.py
+```