code: def double(x):
      return x * 2
  
file_path: lightning-flash/tests/core/serve/test_dag/test_rewrite.py
imports: import pytest
  from flash.core.serve.dag.rewrite import VAR, RewriteRule, RuleSet, Traverser, args, head
  from flash.core.utilities.imports import _TOPIC_SERVE_AVAILABLE
label_desc: Use image node_id 3 for calling a global function with example usage: double(x) and returns: unknown