[3.12] pythongh-120544: Add else: fail() to tests where exception is expected (pythonGH-120545) (python#120547)

pythongh-120544: Add `else: fail()` to tests where exception is expected (pythonGH-120545)
(cherry picked from commit 42ebdd8)

Co-authored-by: Nikita Sobolev <[email protected]>

Author: miss-islington

Lib/test/test_exceptions.py

@@ -1820,6 +1820,8 @@ def f():
         except self.failureException:
             with support.captured_stderr() as err:
                 sys.__excepthook__(*sys.exc_info())
+        else:
+            self.fail("assertRaisesRegex should have failed.")
 
         self.assertIn("aab", err.getvalue())
 

Lib/test/test_unittest/test_case.py

@@ -1132,6 +1132,8 @@ def testAssertMultiLineEqual(self):
             # need to remove the first line of the error message
             error = str(e).split('\n', 1)[1]
             self.assertEqual(sample_text_error, error)
+        else:
+            self.fail(f'{self.failureException} not raised')
 
     def testAssertEqualSingleLine(self):
         sample_text = "laden swallows fly slowly"
@@ -1148,6 +1150,8 @@ def testAssertEqualSingleLine(self):
             # need to remove the first line of the error message
             error = str(e).split('\n', 1)[1]
             self.assertEqual(sample_text_error, error)
+        else:
+            self.fail(f'{self.failureException} not raised')
 
     def testAssertEqualwithEmptyString(self):
         '''Verify when there is an empty string involved, the diff output
@@ -1165,6 +1169,8 @@ def testAssertEqualwithEmptyString(self):
             # need to remove the first line of the error message
             error = str(e).split('\n', 1)[1]
             self.assertEqual(sample_text_error, error)
+        else:
+            self.fail(f'{self.failureException} not raised')
 
     def testAssertEqualMultipleLinesMissingNewlineTerminator(self):
         '''Verifying format of diff output from assertEqual involving strings
@@ -1185,6 +1191,8 @@ def testAssertEqualMultipleLinesMissingNewlineTerminator(self):
             # need to remove the first line of the error message
             error = str(e).split('\n', 1)[1]
             self.assertEqual(sample_text_error, error)
+        else:
+            self.fail(f'{self.failureException} not raised')
 
     def testAssertEqualMultipleLinesMismatchedNewlinesTerminators(self):
         '''Verifying format of diff output from assertEqual involving strings
@@ -1208,6 +1216,8 @@ def testAssertEqualMultipleLinesMismatchedNewlinesTerminators(self):
             # need to remove the first line of the error message
             error = str(e).split('\n', 1)[1]
             self.assertEqual(sample_text_error, error)
+        else:
+            self.fail(f'{self.failureException} not raised')
 
     def testEqualityBytesWarning(self):
         if sys.flags.bytes_warning: