call site 20 for magic.revert
magic/testing/test_patch.py - line 23
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   def test_double_patch():
       class a:
           i = 42
       assert patch(a, 'i', 2) == 42
       assert patch(a, 'i', 3) == 2
       assert a.i == 3
       assert revert(a, 'i') == 3
       assert a.i == 2
->     assert revert(a, 'i') == 2
       assert a.i == 42