add test on variables that have been overwritten are cleared after each test

src/_pytest/assertion/rewrite.py

@@ -657,7 +657,7 @@ class AssertionRewriter(ast.NodeVisitor):
         else:
             self.enable_assertion_pass_hook = False
         self.source = source
-        self.overwrite: Dict[str, str] = {}
+        self.variables_overwrite: Dict[str, str] = {}
 
     def run(self, mod: ast.Module) -> None:
         """Find all assert statements in *mod* and rewrite them."""
@@ -982,7 +982,7 @@ class AssertionRewriter(ast.NodeVisitor):
                 self.expl_stmts.append(ast.If(cond, fail_inner, []))  # noqa
                 self.expl_stmts = fail_inner
                 if isinstance(v, ast.Compare):
-                    if isinstance(v.left, ast.NamedExpr) and (
+                    if isinstance(v.left, namedExpr) and (
                         v.left.target.id
                         in [
                             ast_expr.id
@@ -992,7 +992,7 @@ class AssertionRewriter(ast.NodeVisitor):
                         or v.left.target.id == pytest_temp
                     ):
                         pytest_temp = f"pytest_{v.left.target.id}_temp"
-                        self.overwrite[v.left.target.id] = pytest_temp
+                        self.variables_overwrite[v.left.target.id] = pytest_temp
                         v.left.target.id = pytest_temp
 
                     elif isinstance(v.left, ast.Name) and (
@@ -1075,8 +1075,8 @@ class AssertionRewriter(ast.NodeVisitor):
 
     def visit_Compare(self, comp: ast.Compare) -> Tuple[ast.expr, str]:
         self.push_format_context()
-        if isinstance(comp.left, ast.Name) and comp.left.id in self.overwrite:
-            comp.left.id = self.overwrite[comp.left.id]
+        if isinstance(comp.left, ast.Name) and comp.left.id in self.variables_overwrite:
+            comp.left.id = self.variables_overwrite[comp.left.id]
         left_res, left_expl = self.visit(comp.left)
         if isinstance(comp.left, (ast.Compare, ast.BoolOp)):
             left_expl = f"({left_expl})"
@@ -1089,12 +1089,12 @@ class AssertionRewriter(ast.NodeVisitor):
         results = [left_res]
         for i, op, next_operand in it:
             if (
-                isinstance(next_operand, ast.NamedExpr)
+                isinstance(next_operand, namedExpr)
                 and isinstance(left_res, ast.Name)
                 and next_operand.target.id == left_res.id
             ):
                 next_operand.target.id = f"pytest_{left_res.id}_temp"
-                self.overwrite[left_res.id] = next_operand.target.id
+                self.variables_overwrite[left_res.id] = next_operand.target.id
             next_res, next_expl = self.visit(next_operand)
             if isinstance(next_operand, (ast.Compare, ast.BoolOp)):
                 next_expl = f"({next_expl})"

testing/test_assertrewrite.py

@@ -1418,6 +1418,23 @@ class TestIssue10743:
         assert result.ret == 1
         result.stdout.fnmatch_lines(["*assert not (True and None is None)"])
 
+    def test_assertion_walrus_operator_value_changes_cleared_after_each_test(
+        self, pytester: Pytester
+    ) -> None:
+        pytester.makepyfile(
+            """
+            def test_walrus_operator_change_value():
+                a = True
+                assert (a := None) is None
+
+            def test_walrus_operator_not_override_value():
+                a = True
+                assert a is True
+        """
+        )
+        result = pytester.runpytest()
+        assert result.ret == 0
+
 
 @pytest.mark.skipif(
     sys.maxsize <= (2**31 - 1), reason="Causes OverflowError on 32bit systems"