MDEV-10182 Bad value when inserting COALESCE(CURRENT_TIMESTAMP) into a DECIMAL column

This problem was earlier fixed by the patch cb16d753
for MDEV-11337 Split Item::save_in_field() into virtual methods in Type_handler.

Adding tests only.

mysql-test/main/func_time_hires.result

@@ -206,3 +206,22 @@ time(f1)
 21:00:00.000000
 21:00:01.000000
 drop table t1;
+#
+# Start of 10.3 tests
+#
+#
+# MDEV-10182 Bad value when inserting COALESCE(CURRENT_TIMESTAMP) into a DECIMAL column
+#
+SET timestamp=UNIX_TIMESTAMP('2001-01-01 10:20:30.000000');
+CREATE TABLE t1 (a DECIMAL(30,0));
+INSERT INTO t1 VALUES (CURRENT_TIMESTAMP(6));
+INSERT INTO t1 VALUES (COALESCE(CURRENT_TIMESTAMP(6)));
+SELECT * FROM t1;
+a
+20010101102030
+20010101102030
+DROP TABLE t1;
+SET timestamp=DEFAULT;
+#
+# End of 10.3 tests
+#

mysql-test/main/func_time_hires.test

@@ -106,3 +106,24 @@ alter table t1 modify f1 varchar(100);
 select time(f1) from t1;
 select time(f1) from t1 union all select time(f1 + interval 1 second) from t1;
 drop table t1;
+
+
+--echo #
+--echo # Start of 10.3 tests
+--echo #
+
+--echo #
+--echo # MDEV-10182 Bad value when inserting COALESCE(CURRENT_TIMESTAMP) into a DECIMAL column
+--echo #
+
+SET timestamp=UNIX_TIMESTAMP('2001-01-01 10:20:30.000000');
+CREATE TABLE t1 (a DECIMAL(30,0));
+INSERT INTO t1 VALUES (CURRENT_TIMESTAMP(6));
+INSERT INTO t1 VALUES (COALESCE(CURRENT_TIMESTAMP(6)));
+SELECT * FROM t1;
+DROP TABLE t1;
+SET timestamp=DEFAULT;
+
+--echo #
+--echo # End of 10.3 tests
+--echo #