use assert[Not]In where appropriate
diff --git a/Lib/test/test_multibytecodec.py b/Lib/test/test_multibytecodec.py
index b482b39..e4e86ff 100644
--- a/Lib/test/test_multibytecodec.py
+++ b/Lib/test/test_multibytecodec.py
@@ -242,7 +242,7 @@
         self.assertEqual(iso2022jp2.decode('iso2022-jp-2'), uni)
 
     def test_iso2022_jp_g0(self):
-        self.assertFalse(b'\x0e' in '\N{SOFT HYPHEN}'.encode('iso-2022-jp-2'))
+        self.assertNotIn(b'\x0e', '\N{SOFT HYPHEN}'.encode('iso-2022-jp-2'))
         for encoding in ('iso-2022-jp-2004', 'iso-2022-jp-3'):
             e = '\u3406'.encode(encoding)
             self.assertFalse(any(x > 0x80 for x in e))