bpo-39385: Add an assertNoLogs context manager to unittest.TestCase (GH-18067)

Co-authored-by: Rémi Lapeyre <remi.lapeyre@henki.fr>

Lib/unittest/test/test_case.py

@@ -1681,6 +1681,81 @@ test case
                 with self.assertLogs('foo'):
                     log_quux.error("1")
 
+    def testAssertLogsUnexpectedException(self):
+        # Check unexpected exception will go through.
+        with self.assertRaises(ZeroDivisionError):
+            with self.assertLogs():
+                raise ZeroDivisionError("Unexpected")
+
+    def testAssertNoLogsDefault(self):
+        with self.assertRaises(self.failureException) as cm:
+            with self.assertNoLogs():
+                log_foo.info("1")
+                log_foobar.debug("2")
+        self.assertEqual(
+            str(cm.exception),
+            "Unexpected logs found: ['INFO:foo:1']",
+        )
+
+    def testAssertNoLogsFailureFoundLogs(self):
+        with self.assertRaises(self.failureException) as cm:
+            with self.assertNoLogs():
+                log_quux.error("1")
+                log_foo.error("foo")
+
+        self.assertEqual(
+            str(cm.exception),
+            "Unexpected logs found: ['ERROR:quux:1', 'ERROR:foo:foo']",
+        )
+
+    def testAssertNoLogsPerLogger(self):
+        with self.assertNoStderr():
+            with self.assertLogs(log_quux):
+                with self.assertNoLogs(logger=log_foo):
+                    log_quux.error("1")
+
+    def testAssertNoLogsFailurePerLogger(self):
+        # Failure due to unexpected logs for the given logger or its
+        # children.
+        with self.assertRaises(self.failureException) as cm:
+            with self.assertLogs(log_quux):
+                with self.assertNoLogs(logger=log_foo):
+                    log_quux.error("1")
+                    log_foobar.info("2")
+        self.assertEqual(
+            str(cm.exception),
+            "Unexpected logs found: ['INFO:foo.bar:2']",
+        )
+
+    def testAssertNoLogsPerLevel(self):
+        # Check per-level filtering
+        with self.assertNoStderr():
+            with self.assertNoLogs(level="ERROR"):
+                log_foo.info("foo")
+                log_quux.debug("1")
+
+    def testAssertNoLogsFailurePerLevel(self):
+        # Failure due to unexpected logs at the specified level.
+        with self.assertRaises(self.failureException) as cm:
+            with self.assertNoLogs(level="DEBUG"):
+                log_foo.debug("foo")
+                log_quux.debug("1")
+        self.assertEqual(
+            str(cm.exception),
+            "Unexpected logs found: ['DEBUG:foo:foo', 'DEBUG:quux:1']",
+        )
+
+    def testAssertNoLogsUnexpectedException(self):
+        # Check unexpected exception will go through.
+        with self.assertRaises(ZeroDivisionError):
+            with self.assertNoLogs():
+                raise ZeroDivisionError("Unexpected")
+
+    def testAssertNoLogsYieldsNone(self):
+        with self.assertNoLogs() as value:
+            pass
+        self.assertIsNone(value)
+
     def testDeprecatedMethodNames(self):
         """
         Test that the deprecated methods raise a DeprecationWarning. See #9424.