Re-enable testing of builtin open() in test_bufio in test_largefile
diff --git a/Lib/test/test_bufio.py b/Lib/test/test_bufio.py
index b2c1bf8..48cc0f3 100644
--- a/Lib/test/test_bufio.py
+++ b/Lib/test/test_bufio.py
@@ -68,9 +68,12 @@
 class PyBufferSizeTest(BufferSizeTest):
     open = staticmethod(pyio.open)
 
+class BuiltinBufferSizeTest(BufferSizeTest):
+    open = open
+
 
 def test_main():
-    support.run_unittest(CBufferSizeTest, PyBufferSizeTest)
+    support.run_unittest(CBufferSizeTest, PyBufferSizeTest, BuiltinBufferSizeTest)
 
 if __name__ == "__main__":
     test_main()