bpo-42934: use TracebackException(compact=True) in unittest.TestResult (GH-24221)

Author: iritkatriel

Lib/unittest/result.py

@@ -183,7 +183,8 @@ def _exc_info_to_string(self, err, test):
         else:
             length = None
         tb_e = traceback.TracebackException(
-            exctype, value, tb, limit=length, capture_locals=self.tb_locals)
+            exctype, value, tb,
+            limit=length, capture_locals=self.tb_locals, compact=True)
         msgLines = list(tb_e.format())
 
         if self.buffer:

Misc/NEWS.d/next/Library/2021-01-15-11-48-00.bpo-42934.ILKoOI.rst

@@ -0,0 +1,3 @@
+Use :class:`~traceback.TracebackException`'s new ``compact`` param in
+:class:`~unittest.TestResult` to reduce time and memory consumed by
+traceback formatting.