Use utf8mb4 in test_binary_prefix (#501)

Author: methane

tests/test_MySQLdb_capabilities.py

@@ -182,19 +182,19 @@ def test_binary_prefix(self):
         for binary_prefix in (True, False, None):
             kwargs = self.connect_kwargs.copy()
             # needs to be set to can guarantee CHARSET response for normal strings
-            kwargs["charset"] = "utf8"
+            kwargs["charset"] = "utf8mb4"
             if binary_prefix is not None:
                 kwargs["binary_prefix"] = binary_prefix
 
             with closing(connection_factory(**kwargs)) as conn:
                 with closing(conn.cursor()) as c:
                     c.execute("SELECT CHARSET(%s)", (MySQLdb.Binary(b"raw bytes"),))
                     self.assertEqual(
-                        c.fetchall()[0][0], "binary" if binary_prefix else "utf8"
+                        c.fetchall()[0][0], "binary" if binary_prefix else "utf8mb4"
                     )
                     # normal strings should not get prefix
                     c.execute("SELECT CHARSET(%s)", ("str",))
-                    self.assertEqual(c.fetchall()[0][0], "utf8")
+                    self.assertEqual(c.fetchall()[0][0], "utf8mb4")
 
 
 if __name__ == "__main__":