updates test dependencies (#387)

Author: brichet

CONTRIBUTING.md

@@ -28,7 +28,7 @@ To create a local test setup run the following commands (inside your virtual env
 git clone https://github.com/jupyterlab/jupyterlab_server.git
 cd jupyterlab_server
 pip install -e .[test]  # install test dependencies
-pytest --pyargs jupyterlab_server
+hatch run cov:test # optionally, arguments of the pytest CLI can be added
 ```
 
 ## Code Styling

pyproject.toml

@@ -71,6 +71,7 @@ openapi = [
 ]
 test = [
   "codecov",
+  "hatch",
   "ipykernel",
   "pytest-jupyter[server]>=0.6.2",
   "jupyterlab_server[openapi]",