Tests for MDEV-15881 Assertion `is_valid_value_slow()' failed in Datetime::Datetime or corrupt data after ALTER with indexed persistent column

The patch for "MDEV-18486 Database crash on a table with indexed virtual column"
fixed MDEV-15881 as well. So adding tests only.

Author: abarkov

mysql-test/suite/vcol/r/vcol_keys_myisam.result

@@ -383,3 +383,28 @@ select * from t1;
 id	hexid
 100	64
 drop table t1;
+#
+#  MDEV-15881 Assertion `is_valid_value_slow()' failed in Datetime::Datetime or corrupt data after ALTER with indexed persistent column
+#
+CREATE TABLE t1 (i INT, d1 DATE, d2 DATE NOT NULL, t TIMESTAMP, KEY(t)) ENGINE=MyISAM;
+INSERT INTO t1 VALUES  (1,'2023-03-16','2023-03-15','2012-12-12 12:12:12');
+ALTER TABLE t1 MODIFY t FLOAT AS (i) PERSISTENT;
+SELECT i, d1, d2 FROM t1 INTO OUTFILE 'load_t1';
+DELETE FROM t1;
+LOAD DATA INFILE 'load_t1' INTO TABLE t1 (i,d1,d2);
+SELECT * FROM t1 WHERE d2 < d1;
+i	d1	d2	t
+1	2023-03-16	2023-03-15	1
+DROP TABLE t1;
+CREATE TABLE t1 (
+i INT DEFAULT NULL,
+d1 DATE DEFAULT NULL,
+d2 DATE NOT NULL,
+t FLOAT GENERATED ALWAYS AS (i) STORED,
+KEY (t)
+) ENGINE=MyISAM;
+LOAD DATA INFILE 'load_t1' INTO TABLE t1 (i,d1,d2);
+SELECT * FROM t1 WHERE d2 < d1;
+i	d1	d2	t
+1	2023-03-16	2023-03-15	1
+DROP TABLE t1;

mysql-test/suite/vcol/t/vcol_keys_myisam.test

@@ -272,3 +272,31 @@ create table t1 ( id int primary key,
 insert into t1 (id) select 100;
 select * from t1;
 drop table t1;
+
+
+--echo #
+--echo #  MDEV-15881 Assertion `is_valid_value_slow()' failed in Datetime::Datetime or corrupt data after ALTER with indexed persistent column
+--echo #
+
+CREATE TABLE t1 (i INT, d1 DATE, d2 DATE NOT NULL, t TIMESTAMP, KEY(t)) ENGINE=MyISAM;
+INSERT INTO t1 VALUES  (1,'2023-03-16','2023-03-15','2012-12-12 12:12:12');
+ALTER TABLE t1 MODIFY t FLOAT AS (i) PERSISTENT;
+SELECT i, d1, d2 FROM t1 INTO OUTFILE 'load_t1';
+DELETE FROM t1;
+LOAD DATA INFILE 'load_t1' INTO TABLE t1 (i,d1,d2);
+SELECT * FROM t1 WHERE d2 < d1;
+DROP TABLE t1;
+
+CREATE TABLE t1 (
+  i INT DEFAULT NULL,
+  d1 DATE DEFAULT NULL,
+  d2 DATE NOT NULL,
+  t FLOAT GENERATED ALWAYS AS (i) STORED,
+  KEY (t)
+) ENGINE=MyISAM;
+LOAD DATA INFILE 'load_t1' INTO TABLE t1 (i,d1,d2);
+SELECT * FROM t1 WHERE d2 < d1;
+DROP TABLE t1;
+# Cleanup
+--let $datadir= `SELECT @@datadir`
+--remove_file $datadir/test/load_t1