test: add functional test for TestShell (matching doc example)

test/functional/test_runner.py

@@ -360,6 +360,7 @@ BASE_SCRIPTS = [
     'rpc_getdescriptorinfo.py',
     'rpc_mempool_info.py',
     'rpc_help.py',
+    'feature_framework_testshell.py',
     'tool_rpcauth.py',
     'p2p_handshake.py',
     'p2p_handshake.py --v2transport',