Issue 11510: Fix BUILD_SET optimizer bug.
diff --git a/Lib/test/test_peepholer.py b/Lib/test/test_peepholer.py
index a9eb23f..a40b4b7 100644
--- a/Lib/test/test_peepholer.py
+++ b/Lib/test/test_peepholer.py
@@ -294,11 +294,23 @@
             self.assertNotIn('BINARY_', asm, e)
             self.assertNotIn('BUILD_', asm, e)
 
+class TestBuglets(unittest.TestCase):
+
+     def test_bug_11510(self):
+         # folded constant set optimization was commingled with the tuple
+         # unpacking optimization which would fail if the set had duplicate
+         # elements so that the set length was unexpected
+         def f():
+             x, y = {1, 1}
+             return x, y
+         with self.assertRaises(ValueError):
+             f()
+
 
 def test_main(verbose=None):
     import sys
     from test import support
-    test_classes = (TestTranforms,)
+    test_classes = (TestTranforms, TestBuglets)
     support.run_unittest(*test_classes)
 
     # verify reference counting