Issue #22173: Update lib2to3 tests to use unittest test discovery.
diff --git a/Lib/lib2to3/tests/pytree_idempotency.py b/Lib/lib2to3/tests/pytree_idempotency.py
index 731c403..c6359bf 100755
--- a/Lib/lib2to3/tests/pytree_idempotency.py
+++ b/Lib/lib2to3/tests/pytree_idempotency.py
@@ -4,6 +4,8 @@
 
 """Main program for testing the infrastructure."""
 
+from __future__ import print_function
+
 __author__ = "Guido van Rossum <guido@python.org>"
 
 # Support imports (need to be imported first)