Issue #27348: Restore “Exception: None” formatting in traceback module

This fixes a regression caused by revision 73afda5a4e4c. Also reverts the
decimal test workaround added in revision 5f3dd0a2b1ab.

Remove test_without_exception(). According to revision ecaafc32c500, this was
added in Python 2 so that print_exc() would output “None” when called with no
exception set. However print_exc() never worked like this in Python 3, and
the use case is not documented.

Restore TracebackCases class name (instead of SyntaxTracebackCases), because
the class also tests other exceptions.

1 files changed, 12 insertions, 5 deletions

diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
index 549d8d1e97..b4b74d3fcc 100644
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -19,7 +19,7 @@ test_frame = namedtuple('frame', ['f_code', 'f_globals', 'f_locals'])
 test_tb = namedtuple('tb', ['tb_frame', 'tb_lineno', 'tb_next'])
 
 
-class SyntaxTracebackCases(unittest.TestCase):
+class TracebackCases(unittest.TestCase):
     # For now, a very minimal set of tests.  I want to be sure that
     # formatting of SyntaxErrors works based on changes for 2.1.
 
@@ -106,10 +106,6 @@ class SyntaxTracebackCases(unittest.TestCase):
             str_name = '.'.join([X.__module__, X.__qualname__])
         self.assertEqual(err[0], "%s: %s\n" % (str_name, str_value))
 
-    def test_without_exception(self):
-        err = traceback.format_exception_only(None, None)
-        self.assertEqual(err, ['None\n'])
-
     def test_encoded_file(self):
         # Test that tracebacks are correctly printed for encoded source files:
         # - correct line number (Issue2384)
@@ -456,6 +452,17 @@ class BaseExceptionReportingTests:
         msg = self.get_report(e).splitlines()
         self.assertEqual(msg[-2], '              ^')
 
+    def test_message_none(self):
+        # A message that looks like "None" should not be treated specially
+        err = self.get_report(Exception(None))
+        self.assertIn('Exception: None\n', err)
+        err = self.get_report(Exception('None'))
+        self.assertIn('Exception: None\n', err)
+        err = self.get_report(Exception())
+        self.assertIn('Exception\n', err)
+        err = self.get_report(Exception(''))
+        self.assertIn('Exception\n', err)
+
 
 class PyExcReportingTests(BaseExceptionReportingTests, unittest.TestCase):
     #