assertEqual doesn't display newline differences quite well

Lib/unittest/util.py

 """Various utility functions."""
 
 from collections import namedtuple, OrderedDict
 
 __unittest = True
 
 _MAX_LENGTH = 80
-def safe_repr(obj, short=False):
+def safe_repr(obj, short=False, max_length=None):
     try:
         result = repr(obj)
     except Exception:
         result = object.__repr__(obj)
-    if not short or len(result) < _MAX_LENGTH:
+
+    len_result = len(result)
+    truncate_size = max_length or _MAX_LENGTH
+    if not short or len_result <= truncate_size:
         return result
-    return result[:_MAX_LENGTH] + ' [truncated]...'
+
+    if truncate_size <= _MAX_LENGTH:
+        result = result[:truncate_size]
+    else:
+        #  0         _MAX_LENGTH     truncate_size    len(result)
+        #  begin                        trunc             end
+        #  <----------------------------------------------->
+        #  begin   ...   trunc
+        #  <-------------->
+        result = (result[:_MAX_LENGTH // 2] + '...' +
+                  result[-_MAX_LENGTH // 2:truncate_size])
+
+    if truncate_size < len_result:
+        return result + ' [truncated]...'
+    return result
 
 def strclass(cls):
     return "%s.%s" % (cls.__module__, cls.__name__)
 
 def sorted_list_difference(expected, actual):
     """Finds elements in only one or the other of two, sorted input lists.
 
     Returns a two-element tuple of lists.    The first list contains those
     elements in the "expected" list but not in the "actual" list, and the
     second contains those elements in the "actual" list but not in the
@@ skipping 105 matching lines @@
     for elem, cnt_s in s.items():
         cnt_t = t.get(elem, 0)
         if cnt_s != cnt_t:
             diff = _Mismatch(cnt_s, cnt_t, elem)
             result.append(diff)
     for elem, cnt_t in t.items():
         if elem not in s:
             diff = _Mismatch(0, cnt_t, elem)
             result.append(diff)
     return result