Add a test case for r1316 (Bug #25927).

mysql-test/innodb.result

@@ -3471,3 +3471,12 @@ t2	CREATE TABLE `t2` (
   CONSTRAINT `t2_t1` FOREIGN KEY (`id`) REFERENCES `t1` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
 ) ENGINE=InnoDB DEFAULT CHARSET=latin1
 DROP TABLE t2, t1;
+CREATE TABLE t1 (a INT, INDEX(a)) ENGINE=InnoDB;
+CREATE TABLE t2 (a INT, INDEX(a)) ENGINE=InnoDB;
+INSERT INTO t1 VALUES (1);
+INSERT INTO t2 VALUES (1);
+ALTER TABLE t2 ADD FOREIGN KEY (a) REFERENCES t1 (a) ON DELETE SET NULL;
+ALTER TABLE t2 MODIFY a INT NOT NULL;
+ERROR HY000: Error on rename of '#sql-temporary' to './test/t2' (errno: 150)
+DELETE FROM t1;
+DROP TABLE t2,t1;

mysql-test/innodb.test

@@ -2513,6 +2513,22 @@ DELETE CASCADE ON UPDATE CASCADE;
 SHOW CREATE TABLE t2;
 DROP TABLE t2, t1;
 
+#
+# Bug #25927: Prevent ALTER TABLE ... MODIFY ... NOT NULL on columns
+# for which there is a foreign key constraint ON ... SET NULL.
+#
+
+CREATE TABLE t1 (a INT, INDEX(a)) ENGINE=InnoDB;
+CREATE TABLE t2 (a INT, INDEX(a)) ENGINE=InnoDB;
+INSERT INTO t1 VALUES (1);
+INSERT INTO t2 VALUES (1);
+ALTER TABLE t2 ADD FOREIGN KEY (a) REFERENCES t1 (a) ON DELETE SET NULL;
+--replace_regex /'\.\/test\/#sql-[0-9a-f_]*'/'#sql-temporary'/
+--error 1025
+ALTER TABLE t2 MODIFY a INT NOT NULL;
+DELETE FROM t1;
+DROP TABLE t2,t1;
+
 #######################################################################
 #                                                                     #
 # Please, DO NOT TOUCH this file as well as the innodb.result file.   #