Add assertDoesNotAddMessages to CheckerTestCase

doc/whatsnew/fragments/9598.feature

@@ -0,0 +1,3 @@
+Add ``assertDoesNotAddMessages`` to ``CheckerTestCase`` to assert that specific messages are not emitted, while allowing other messages to be present. This complements ``assertNoMessages`` which asserts that no messages at all are emitted.
+
+Closes #9598

pylint/testutils/checker_test_case.py

@@ -37,6 +37,54 @@ def assertNoMessages(self) -> Iterator[None]:
         with self.assertAddsMessages():
             yield
 
+    @contextlib.contextmanager
+    def assertDoesNotAddMessages(
+        self, *messages: MessageTest, ignore_position: bool = False
+    ) -> Generator[None]:
+        """Assert that the given messages are not added by the given method.
+
+        This is different from ``assertNoMessages`` which asserts that no
+        messages at all are added.  ``assertDoesNotAddMessages`` checks that
+        none of the *specific* messages passed as arguments are emitted, while
+        other messages may still be present.
+        """
+        yield
+        got = self.linter.release_messages()
+        for unwanted in messages:
+            for gotten_msg in got:
+                if not self._messages_match(unwanted, gotten_msg, ignore_position):
+                    continue
+                got_str = "\n".join(repr(m) for m in got)
+                msg = (
+                    "Expected the following message to not be raised:\n"
+                    f"\n  {unwanted!r}\n\n"
+                    f"but it was found among the actual messages:\n\n{got_str}\n"
+                )
+                raise AssertionError(msg)
+
+    @staticmethod
+    def _messages_match(
+        expected: MessageTest, actual: MessageTest, ignore_position: bool
+    ) -> bool:
+        if expected.msg_id != actual.msg_id:
+            return False
+        if expected.node != actual.node:
+            return False
+        if expected.args != actual.args:
+            return False
+        if expected.confidence != actual.confidence:
+            return False
+        if not ignore_position:
+            if expected.line != actual.line:
+                return False
+            if expected.col_offset != actual.col_offset:
+                return False
+            if expected.end_line != actual.end_line:
+                return False
+            if expected.end_col_offset != actual.end_col_offset:
+                return False
+        return True
+
     @contextlib.contextmanager
     def assertAddsMessages(
         self, *messages: MessageTest, ignore_position: bool = False

tests/testutils/test_checker_test_case.py

@@ -0,0 +1,96 @@
+# Licensed under the GPL: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
+# For details: https://github.com/pylint-dev/pylint/blob/main/LICENSE
+# Copyright (c) https://github.com/pylint-dev/pylint/blob/main/CONTRIBUTORS.txt
+
+"""Tests for CheckerTestCase assertion methods."""
+
+from __future__ import annotations
+
+import pytest
+
+from pylint.checkers.base_checker import BaseChecker
+from pylint.interfaces import UNDEFINED
+from pylint.testutils import CheckerTestCase, MessageTest
+
+
+class _DummyChecker(BaseChecker):
+    """A minimal checker used only for testing the test infrastructure."""
+
+    name = "dummy-for-testcase"
+    msgs = {
+        "W9901": ("Dummy message A", "dummy-msg-a", "Dummy message A."),
+        "W9902": ("Dummy message B", "dummy-msg-b", "Dummy message B."),
+    }
+
+
+_MSG_A = MessageTest("W9901", line=1, node=None, args=None, confidence=UNDEFINED)
+_MSG_B = MessageTest("W9902", line=2, node=None, args=None, confidence=UNDEFINED)
+
+
+class TestCheckerTestCase(CheckerTestCase):
+    CHECKER_CLASS = _DummyChecker
+
+    # -- assertAddsMessages scenarios (1-3) -----------------------------------
+
+    def test_assert_adds_messages_success(self) -> None:
+        """Scenario 1: expected raised / actual raised."""
+        with self.assertAddsMessages(_MSG_A):
+            self.linter.add_message("W9901", line=1)
+
+    def test_assert_adds_messages_failure_not_raised(self) -> None:
+        """Scenario 2: expected raised / actual not raised."""
+        with pytest.raises(AssertionError):
+            with self.assertAddsMessages(_MSG_A):
+                pass  # nothing emitted
+
+    def test_assert_adds_messages_failure_wrong_message(self) -> None:
+        """Scenario 3: expected raised / actual not raised but another one raised."""
+        with pytest.raises(AssertionError):
+            with self.assertAddsMessages(_MSG_A):
+                self.linter.add_message("W9902", line=2)
+
+    # -- assertDoesNotAddMessages scenarios (4-6) -----------------------------
+
+    def test_assert_does_not_add_messages_failure(self) -> None:
+        """Scenario 4: expected not raised / actual raised."""
+        with pytest.raises(AssertionError):
+            with self.assertDoesNotAddMessages(_MSG_A):
+                self.linter.add_message("W9901", line=1)
+
+    def test_assert_does_not_add_messages_success(self) -> None:
+        """Scenario 5: expected not raised / actual not raised."""
+        with self.assertDoesNotAddMessages(_MSG_A):
+            pass  # nothing emitted
+
+    def test_assert_does_not_add_messages_success_other_raised(self) -> None:
+        """Scenario 6: expected not raised / actual not raised but another one raised."""
+        with self.assertDoesNotAddMessages(_MSG_A):
+            self.linter.add_message("W9902", line=2)
+
+    # -- additional edge cases ------------------------------------------------
+
+    def test_assert_does_not_add_messages_ignore_position(self) -> None:
+        """Position mismatch means no match when ignore_position=False."""
+        # Same msg_id but different line: should pass (not a match)
+        msg_different_line = MessageTest(
+            "W9901", line=99, node=None, args=None, confidence=UNDEFINED
+        )
+        with self.assertDoesNotAddMessages(msg_different_line):
+            self.linter.add_message("W9901", line=1)
+
+    def test_assert_does_not_add_messages_ignore_position_true(self) -> None:
+        """With ignore_position=True, position differences are ignored."""
+        msg_different_line = MessageTest(
+            "W9901", line=99, node=None, args=None, confidence=UNDEFINED
+        )
+        with pytest.raises(AssertionError):
+            with self.assertDoesNotAddMessages(
+                msg_different_line, ignore_position=True
+            ):
+                self.linter.add_message("W9901", line=1)
+
+    def test_assert_does_not_add_messages_multiple_unwanted(self) -> None:
+        """Fails when any of several unwanted messages is found."""
+        with pytest.raises(AssertionError):
+            with self.assertDoesNotAddMessages(_MSG_A, _MSG_B):
+                self.linter.add_message("W9902", line=2)