Issue #12400: runtest() truncates the StringIO stream before a new test

diff --git a/Lib/test/regrtest.py b/Lib/test/regrtest.py
index 75d8795aff944c20274b6cc9904907acac57a30b..f1ef7156103c1368246a8d8bc31dae0d74c6637d 100755 (executable)
--- a/Lib/test/regrtest.py
+++ b/Lib/test/regrtest.py
@@ -793,6 +793,7 @@ def runtest(test, verbose, quiet,
             if runtest.stringio is None:
                 runtest.stringio = io.StringIO()
             stream = runtest.stringio
+            stream.truncate(0)
 
             orig_stdout = sys.stdout
             orig_stderr = sys.stderr