Add a test case for Bug#21704: Renaming column does not update

FK definition.

mysql-test/include/mix1.inc

@@ -1410,4 +1410,33 @@ SELECT * FROM t1 WHERE tid = 1 AND vid = 3 ORDER BY idx DESC;
 
 DROP TABLE t1;
 
+#
+# Bug#21704: Renaming column does not update FK definition.
+#
+
+--disable_warnings
+DROP TABLE IF EXISTS t1;
+DROP TABLE IF EXISTS t2;
+--enable_warnings
+
+CREATE TABLE t1(id INT PRIMARY KEY)
+  ENGINE=innodb;
+
+CREATE TABLE t2(
+  t1_id INT PRIMARY KEY,
+  CONSTRAINT fk1 FOREIGN KEY (t1_id) REFERENCES t1(id))
+  ENGINE=innodb;
+
+--echo
+
+--disable_result_log
+--error ER_ERROR_ON_RENAME
+ALTER TABLE t1 CHANGE id id2 INT;
+--enable_result_log
+
+--echo
+
+DROP TABLE t2;
+DROP TABLE t1;
+
 --echo End of 5.1 tests