Add assertDoesNotAddMessages to CheckerTestCase

doc/whatsnew/fragments/9598.internal

@@ -0,0 +1,6 @@
+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.
+
+Refs #9598

pylint/testutils/checker_test_case.py

@@ -37,6 +37,35 @@ def assertNoMessages(self) -> Iterator[None]:
         with self.assertAddsMessages():
             yield
 
+    @contextlib.contextmanager
+    def assertDoesNotAddMessages(self, *message_ids: str) -> Generator[None]:
+        """Assert that none of the given message IDs are emitted by the checker.
+
+        Unlike ``assertNoMessages``, other messages may still be emitted.
+        Only the specified message IDs are checked to be absent.
+        """
+        if not message_ids:
+            raise TypeError(
+                "assertDoesNotAddMessages requires at least one message ID argument"
+            )
+        exception_raised = False
+        try:
+            yield
+        except Exception:
+            exception_raised = True
+            raise
+        finally:
+            got = self.linter.release_messages()
+            if not exception_raised:
+                emitted_ids = {m.msg_id for m in got}
+                for unwanted_id in message_ids:
+                    if unwanted_id in emitted_ids:
+                        got_str = "\n".join(repr(m) for m in got)
+                        raise AssertionError(
+                            f"Message '{unwanted_id}' was not expected to be emitted"
+                            f" but it was found among the actual messages:\n\n{got_str}\n"
+                        )
+
     @contextlib.contextmanager
     def assertAddsMessages(
         self, *messages: MessageTest, ignore_position: bool = False

tests/testutils/test_checker_test_case.py

@@ -0,0 +1,87 @@
+# 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)
+
+
+class TestCheckerTestCase(CheckerTestCase):
+    CHECKER_CLASS = _DummyChecker
+
+    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, match="..."):
+            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)
+
+    def test_assert_does_not_add_messages_failure(self) -> None:
+        """Scenario 4: expected not raised / actual raised."""
+        with pytest.raises(AssertionError, match="..."):
+            with self.assertDoesNotAddMessages("W9901"):
+                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("W9901"):
+            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("W9901"):
+            self.linter.add_message("W9902", line=2)
+
+    def test_assert_does_not_add_messages_no_args_raises(self) -> None:
+        """Calling with no arguments must raise TypeError."""
+        with pytest.raises(TypeError, match="requires at least one"):
+            with self.assertDoesNotAddMessages():
+                pass
+
+    def test_assert_does_not_add_messages_multiple_unwanted(self) -> None:
+        """Fails when any of the several unwanted message IDs is found."""
+        with pytest.raises(AssertionError, match="..."):
+            with self.assertDoesNotAddMessages("W9901", "W9902"):
+                self.linter.add_message("W9902", line=2)
+
+    def test_assert_does_not_add_messages_exception_in_body_drains_messages(
+        self,
+    ) -> None:
+        """An exception in the with-block must not leak messages to later tests."""
+        with pytest.raises(RuntimeError):
+            with self.assertDoesNotAddMessages("W9901"):
+                self.linter.add_message("W9901", line=1)
+                raise RuntimeError("something went wrong")
+        # Messages must have been drained; a subsequent assertNoMessages should pass.
+        with self.assertNoMessages():
+            pass