[test] Make test duplication more robust

tools/testrunner/objects/testcase.py

Index: tools/testrunner/objects/testcase.py
diff --git a/tools/testrunner/objects/testcase.py b/tools/testrunner/objects/testcase.py
index ad2a8dedafeda650bb834b1a0e17ecffd80b1578..00722d768b3b44ebed23a9af8ec2524a463b0da5 100644
--- a/tools/testrunner/objects/testcase.py
+++ b/tools/testrunner/objects/testcase.py
@@ -36,7 +36,7 @@ class TestCase(object):
     self.flags = flags or []  # list of strings, flags specific to this test
     self.variant = variant    # name of the used testing variant
     self.override_shell = override_shell
-    self.outcomes = set([])
+    self.outcomes = frozenset([])
     self.output = None
     self.id = None  # int, used to map result back to TestCase instance
     self.duration = None  # assigned during execution
@@ -45,7 +45,7 @@ class TestCase(object):
   def CopyAddingFlags(self, variant, flags):
     copy = TestCase(self.suite, self.path, variant, self.flags + flags,
                     self.override_shell)
-    copy.outcomes = set(self.outcomes)
+    copy.outcomes = self.outcomes
     return copy
 
   def PackTask(self):
@@ -63,7 +63,7 @@ class TestCase(object):
     """Creates a new TestCase object based on packed task data."""
     # For the order of the fields, refer to PackTask() above.
     test = TestCase(str(task[0]), task[1], task[2], task[3], task[4])
-    test.outcomes = set(task[5])
+    test.outcomes = frozenset(task[5])
     test.id = task[6]
     test.run = 1
     return test