Fix match or patterns by only mutating operator BitOr

Author: Otto-AA

mutmut/node_mutation.py

@@ -1,6 +1,6 @@
 """This module contains the mutations for indidvidual nodes, e.g. replacing a != b with a == b."""
 import re
-from typing import Any, Union
+from typing import Any, Union, cast
 from collections.abc import Callable, Iterable, Sequence
 import libcst as cst
 import libcst.matchers as m
@@ -218,7 +218,11 @@ def operator_name(node: cst.Name) -> Iterable[cst.CSTNode]:
 def operator_swap_op(
     node: cst.CSTNode
 ) -> Iterable[cst.CSTNode]:
-    yield from _simple_mutation_mapping(node, _operator_mapping)
+    if m.matches(node, m.BinaryOperation() | m.UnaryOperation() | m.BooleanOperation() | m.ComparisonTarget() | m.AugAssign()):
+        typed_node = cast(Union[cst.BinaryOperation, cst.UnaryOperation, cst.BooleanOperation, cst.ComparisonTarget, cst.AugAssign], node)
+        operator = typed_node.operator
+        for new_operator in _simple_mutation_mapping(operator, _operator_mapping):
+            yield node.with_changes(operator=new_operator)
 
 
 def operator_augmented_assignment(

tests/test_mutation.py

@@ -284,6 +284,19 @@ def test_match_case():
 
     assert sorted(mutants) == sorted(expected)
 
+def test_mach_case_does_not_mutate_bitor():
+    source = """
+def concat():
+    match x:
+        case A() | B():
+            pass
+"""
+
+    mutants = mutants_for_source(source)
+
+    assert sorted(mutants) == []
+
+
 def test_basic_class():
     source = """
 class Foo:
@@ -309,8 +322,8 @@ def test_function_with_annotation():
     print(mutated_code)
 
     expected_defs = [
-        'def x_capitalize__mutmut_1(s : str):\n    return s[1].title() + s[1:] if s else s',
-        'def x_capitalize__mutmut_2(s : str):\n    return s[0].title() - s[1:] if s else s',
+        'def x_capitalize__mutmut_1(s : str):\n    return s[0].title() - s[1:] if s else s',
+        'def x_capitalize__mutmut_2(s : str):\n    return s[1].title() + s[1:] if s else s',
         'def x_capitalize__mutmut_3(s : str):\n    return s[0].title() + s[2:] if s else s',
     ]