    def find_server_extensions(self):
        """
        Overloads a method in jupyter_server's ServerApp class (lab or notebook
        >=7) to conditionally enable a jupyterhub test extension.

        ref: https://github.com/jupyter-server/jupyter_server/blob/v2.2.1/jupyter_server/serverapp.py#L2238
        """
        super().find_server_extensions()
        if os.getenv("JUPYTERHUB_SINGLEUSER_TEST_EXTENSION") == "1":
            self.log.warning("Enabling jupyterhub test extension")
            self.jpserver_extensions["jupyterhub.tests.extension"] = True
Overloads a method in jupyter_server's ServerApp class (lab or notebook
>=7) to conditionally enable a jupyterhub test extension.

ref: https://github.com/jupyter-server/jupyter_server/blob/v2.2.1/jupyter_server/serverapp.py#L2238
jupyterhub/singleuser/mixins.py