bpo-30664: The description of a unittest subtest now preserves the (#2265)

order of keyword arguments of TestCase.subTest().

1 files changed, 12 insertions, 2 deletions

diff --git a/Lib/unittest/case.py b/Lib/unittest/case.py
index 993aaec..f19afef 100644
--- a/Lib/unittest/case.py
+++ b/Lib/unittest/case.py
@@ -338,6 +338,16 @@ class _AssertLogsContext(_BaseTestCaseContext):
                 .format(logging.getLevelName(self.level), self.logger.name))
 
 
+class _OrderedChainMap(collections.ChainMap):
+    def __iter__(self):
+        seen = set()
+        for mapping in self.maps:
+            for k in mapping:
+                if k not in seen:
+                    seen.add(k)
+                    yield k
+
+
 class TestCase(object):
     """A class whose instances are single test cases.
 
@@ -514,7 +524,7 @@ class TestCase(object):
             return
         parent = self._subtest
         if parent is None:
-            params_map = collections.ChainMap(params)
+            params_map = _OrderedChainMap(params)
         else:
             params_map = parent.params.new_child(params)
         self._subtest = _SubTest(self, msg, params_map)
@@ -1418,7 +1428,7 @@ class _SubTest(TestCase):
         if self.params:
             params_desc = ', '.join(
                 "{}={!r}".format(k, v)
-                for (k, v) in sorted(self.params.items()))
+                for (k, v) in self.params.items())
             parts.append("({})".format(params_desc))
         return " ".join(parts) or '(<subtest>)'