add visit_NamedExpr in assertrewrite

src/_pytest/assertion/rewrite.py

@@ -666,7 +666,7 @@ class AssertionRewriter(ast.NodeVisitor):
         if doc is not None and self.is_rewrite_disabled(doc):
             return
         pos = 0
-        lineno = 1
+        item = None
         for item in mod.body:
             if (
                 expect_docstring
@@ -937,6 +937,17 @@ class AssertionRewriter(ast.NodeVisitor):
                 ast.copy_location(node, assert_)
         return self.statements
 
+    def visit_NamedExpr(self, name: ast.NamedExpr) -> Tuple[ast.NamedExpr, str]:
+        # Display the repr of the target name if it's a local variable or
+        # _should_repr_global_name() thinks it's acceptable.
+        locs = ast.Call(self.builtin("locals"), [], [])
+        target_id = name.target.id  # type: ignore[attr-defined]
+        inlocs = ast.Compare(ast.Str(target_id), [ast.In()], [locs])
+        dorepr = self.helper("_should_repr_global_name", name)
+        test = ast.BoolOp(ast.Or(), [inlocs, dorepr])
+        expr = ast.IfExp(test, self.display(name), ast.Str(target_id))
+        return name, self.explanation_param(expr)
+
     def visit_Name(self, name: ast.Name) -> Tuple[ast.Name, str]:
         # Display the repr of the name if it's a local variable or
         # _should_repr_global_name() thinks it's acceptable.
@@ -1050,7 +1061,7 @@ class AssertionRewriter(ast.NodeVisitor):
         results = [left_res]
         for i, op, next_operand in it:
             next_res, next_expl = self.visit(next_operand)
-            if isinstance(next_operand, (ast.Compare, ast.BoolOp)):
+            if isinstance(next_operand, (ast.Compare, ast.BoolOp, ast.NamedExpr)):
                 next_expl = f"({next_expl})"
             results.append(next_res)
             sym = BINOP_MAP[op.__class__]
@@ -1072,6 +1083,7 @@ class AssertionRewriter(ast.NodeVisitor):
             res: ast.expr = ast.BoolOp(ast.And(), load_names)
         else:
             res = load_names[0]
+
         return res, self.explanation_param(self.pop_format_context(expl_call))
 
 

testing/test_assertrewrite.py

@@ -1265,6 +1265,160 @@ class TestIssue2121:
         result.stdout.fnmatch_lines(["*E*assert (1 + 1) == 3"])
 
 
+class TestIssue10743:
+    def test_assertion_walrus_operator(self, pytester: Pytester) -> None:
+        pytester.makepyfile(
+            """
+            def my_func(before, after):
+                return before == after
+
+            def change_value(value):
+                return value.lower()
+
+            def test_walrus_conversion():
+                a = "Hello"
+                assert not my_func(a, a := change_value(a))
+                assert a == "hello"
+        """
+        )
+        result = pytester.runpytest()
+        assert result.ret == 0
+
+    def test_assertion_walrus_operator_dont_rewrite(self, pytester: Pytester) -> None:
+        pytester.makepyfile(
+            """
+            'PYTEST_DONT_REWRITE'
+            def my_func(before, after):
+                return before == after
+
+            def change_value(value):
+                return value.lower()
+
+            def test_walrus_conversion_dont_rewrite():
+                a = "Hello"
+                assert not my_func(a, a := change_value(a))
+                assert a == "hello"
+        """
+        )
+        result = pytester.runpytest()
+        assert result.ret == 0
+
+    def test_assertion_inline_walrus_operator(self, pytester: Pytester) -> None:
+        pytester.makepyfile(
+            """
+            def my_func(before, after):
+                return before == after
+
+            def test_walrus_conversion_inline():
+                a = "Hello"
+                assert not my_func(a, a := a.lower())
+                assert a == "hello"
+        """
+        )
+        result = pytester.runpytest()
+        assert result.ret == 0
+
+    def test_assertion_inline_walrus_operator_reverse(self, pytester: Pytester) -> None:
+        pytester.makepyfile(
+            """
+            def my_func(before, after):
+                return before == after
+
+            def test_walrus_conversion_reverse():
+                a = "Hello"
+                assert my_func(a := a.lower(), a)
+                assert a == 'hello'
+        """
+        )
+        result = pytester.runpytest()
+        assert result.ret == 0
+
+    def test_assertion_walrus_no_variable_name_conflict(
+        self, pytester: Pytester
+    ) -> None:
+        pytester.makepyfile(
+            """
+            def test_walrus_conversion_no_conflict():
+                a = "Hello"
+                assert a == (b := a.lower())
+        """
+        )
+        result = pytester.runpytest()
+        assert result.ret == 1
+        result.stdout.fnmatch_lines(["*AssertionError: assert 'Hello' == 'hello'"])
+
+    def test_assertion_walrus_operator_true_assertion_and_changes_variable_value(
+        self, pytester: Pytester
+    ) -> None:
+        pytester.makepyfile(
+            """
+            def test_walrus_conversion_succeed():
+                a = "Hello"
+                assert a != (a := a.lower())
+                assert a == 'hello'
+        """
+        )
+        result = pytester.runpytest()
+        assert result.ret == 0
+
+    def test_assertion_walrus_operator_fail_assertion(self, pytester: Pytester) -> None:
+        pytester.makepyfile(
+            """
+            def test_walrus_conversion_fails():
+                a = "Hello"
+                assert a == (a := a.lower())
+        """
+        )
+        result = pytester.runpytest()
+        assert result.ret == 1
+        # This is not optimal as error message but it depends on how the rewrite is structured
+        result.stdout.fnmatch_lines(["*AssertionError: assert 'hello' == 'hello'"])
+
+    def test_assertion_walrus_operator_boolean_composite(
+        self, pytester: Pytester
+    ) -> None:
+        pytester.makepyfile(
+            """
+            def test_walrus_operator_change_boolean_value():
+                a = True
+                assert a and True and ((a := False) is False) and (a is False) and ((a := None) is None)
+
+        """
+        )
+        result = pytester.runpytest()
+        assert result.ret == 0
+
+    def test_assertion_walrus_operator_compare_boolean_fails(
+        self, pytester: Pytester
+    ) -> None:
+        pytester.makepyfile(
+            """
+            def test_walrus_operator_change_boolean_value():
+                a = True
+                assert not (a and ((a := False) is False))
+        """
+        )
+        result = pytester.runpytest()
+        assert result.ret == 1
+        # This is not optimal as error message but it depends on how the rewrite is structured
+        result.stdout.fnmatch_lines(["*assert not (False)"])
+
+    def test_assertion_walrus_operator_boolean_none_fails(
+        self, pytester: Pytester
+    ) -> None:
+        pytester.makepyfile(
+            """
+            def test_walrus_operator_change_boolean_value():
+                a = True
+                assert not (a and ((a := None) is None))
+        """
+        )
+        result = pytester.runpytest()
+        assert result.ret == 1
+        # This is not optimal as error message but it depends on how the rewrite is structured
+        result.stdout.fnmatch_lines(["*assert not (None)"])
+
+
 @pytest.mark.skipif(
     sys.maxsize <= (2**31 - 1), reason="Causes OverflowError on 32bit systems"
 )