bpo-34945: Buffer output in test suite only when creating junit file

Lib/test/support/__init__.py

@@ -1921,10 +1921,9 @@ def _filter_suite(suite, pred):
 
 def _run_suite(suite):
     """Run tests from a unittest.TestSuite-derived class."""
-    runner = get_test_runner(sys.stdout, verbosity=verbose)
-
-    # TODO: Remove this before merging (here for easy comparison with old impl)
-    #runner = unittest.TextTestRunner(sys.stdout, verbosity=2, failfast=failfast)
+    runner = get_test_runner(sys.stdout,
+                             verbosity=verbose,
+                             capture_output=(junit_xml_list is not None))
 
     result = runner.run(suite)
 

Lib/test/support/testresult.py

@@ -60,10 +60,12 @@ def _add_result(self, test, capture=False, **args):
             e.set('time', f'{time.perf_counter() - self.__start_time:0.6f}')
 
         if capture:
-            stdout = self._stdout_buffer.getvalue().rstrip()
-            ET.SubElement(e, 'system-out').text = stdout
-            stderr = self._stderr_buffer.getvalue().rstrip()
-            ET.SubElement(e, 'system-err').text = stderr
+            if self._stdout_buffer is not None:
+                stdout = self._stdout_buffer.getvalue().rstrip()
+                ET.SubElement(e, 'system-out').text = stdout
+            if self._stderr_buffer is not None:
+                stderr = self._stderr_buffer.getvalue().rstrip()
+                ET.SubElement(e, 'system-err').text = stderr
 
         for k, v in args.items():
             if not k or not v:
@@ -152,23 +154,24 @@ def get_xml_element(self):
         return e
 
 class QuietRegressionTestRunner:
-    def __init__(self, stream):
+    def __init__(self, stream, buffer=False):
         self.result = RegressionTestResult(stream, None, 0)
+        self.result.buffer = buffer
 
     def run(self, test):
         test(self.result)
         return self.result
 
-def get_test_runner_class(verbosity):
+def get_test_runner_class(verbosity, buffer=False):
     if verbosity:
         return functools.partial(unittest.TextTestRunner,
                                  resultclass=RegressionTestResult,
-                                 buffer=True,
+                                 buffer=buffer,
                                  verbosity=verbosity)
-    return QuietRegressionTestRunner
+    return functools.partial(QuietRegressionTestRunner, buffer=buffer)
 
-def get_test_runner(stream, verbosity):
-    return get_test_runner_class(verbosity)(stream)
+def get_test_runner(stream, verbosity, capture_output=False):
+    return get_test_runner_class(verbosity, capture_output)(stream)
 
 if __name__ == '__main__':
     class TestTests(unittest.TestCase):