1 files changed, 39 insertions, 1 deletions
diff --git a/lib/testtools/testtools/testsuite.py b/lib/testtools/testtools/testsuite.py
index 41eb6f7d3a..67ace56110 100644
--- a/lib/testtools/testtools/testsuite.py
+++ b/lib/testtools/testtools/testsuite.py
@@ -6,9 +6,10 @@ __metaclass__ = type
 __all__ = [
   'ConcurrentTestSuite',
   'iterate_tests',
+  'sorted_tests',
   ]
 
-from testtools.helpers import try_imports
+from testtools.helpers import safe_hasattr, try_imports
 
 Queue = try_imports(['Queue.Queue', 'queue.Queue'])
 
@@ -114,3 +115,40 @@ class FixtureSuite(unittest.TestSuite):
             super(FixtureSuite, self).run(result)
         finally:
             self._fixture.cleanUp()
+
+    def sort_tests(self):
+        self._tests = sorted_tests(self, True)
+
+
+def _flatten_tests(suite_or_case, unpack_outer=False):
+    try:
+        tests = iter(suite_or_case)
+    except TypeError:
+        # Not iterable, assume it's a test case.
+        return [(suite_or_case.id(), suite_or_case)]
+    if (type(suite_or_case) in (unittest.TestSuite,) or
+        unpack_outer):
+        # Plain old test suite (or any others we may add).
+        result = []
+        for test in tests:
+            # Recurse to flatten.
+            result.extend(_flatten_tests(test))
+        return result
+    else:
+        # Find any old actual test and grab its id.
+        suite_id = None
+        tests = iterate_tests(suite_or_case)
+        for test in tests:
+            suite_id = test.id()
+            break
+        # If it has a sort_tests method, call that.
+        if safe_hasattr(suite_or_case, 'sort_tests'):
+            suite_or_case.sort_tests()
+        return [(suite_id, suite_or_case)]
+
+
+def sorted_tests(suite_or_case, unpack_outer=False):
+    """Sort suite_or_case while preserving non-vanilla TestSuites."""
+    tests = _flatten_tests(suite_or_case, unpack_outer=unpack_outer)
+    tests.sort()
+    return unittest.TestSuite([test for (sort_key, test) in tests])