Silence some py3k warnings claiming to affect _pyio

Lib/test/test_memoryio.py

@@ -129,7 +129,9 @@ class MemoryTestMixin:
         pos = memio.tell()
         self.assertEqual(memio.truncate(None), pos)
         self.assertEqual(memio.tell(), pos)
-        self.assertRaises(TypeError, memio.truncate, '0')
+        # Silence a py3k warning
+        with support.check_warnings():
+            self.assertRaises(TypeError, memio.truncate, '0')
         memio.close()
         self.assertRaises(ValueError, memio.truncate, 0)
 
@@ -165,7 +167,9 @@ class MemoryTestMixin:
         self.assertEqual(type(memio.read()), type(buf))
         memio.seek(0)
         self.assertEqual(memio.read(None), buf)
-        self.assertRaises(TypeError, memio.read, '')
+        # Silence a py3k warning
+        with support.check_warnings():
+            self.assertRaises(TypeError, memio.read, '')
         memio.close()
         self.assertRaises(ValueError, memio.read)