code: def test_RewriteRule():
      # Test extraneous vars are removed, varlist is correct
      assert rule1.vars == ("a",)
      assert rule1._varlist == ["a"]
      assert rule2.vars == ("a",)
      assert rule2._varlist == ["a", "a"]
      assert rule3.vars == ("a",)
      assert rule3._varlist == ["a", "a"]
      assert rule4.vars == ("a", "b")
      assert rule4._varlist == ["b", "a"]
      assert rule5.vars == ("a", "b", "c")
      assert rule5._varlist == ["c", "b", "a"]
  
file_path: dask/dask/tests/test_rewrite.py
imports: from __future__ import annotations
  from dask.rewrite import VAR, RewriteRule, RuleSet, Traverser, args, head
  from dask.utils_test import add, inc
label_desc: Use image node_id 6 for calling a global function with example usage: test_RewriteRule() without return types