add concat_ws function compatibility test case

src/test/regress/expected/pg_compatibility.out

@@ -28,4 +28,18 @@ select ''::int;
 ERROR:  invalid input syntax for integer: ""
 LINE 1: select ''::int;
                ^
-CONTEXT:  referenced column: int4
+CONTEXT:  referenced column: int4
+
+select concat_ws('','ABCDE', 2, null, 22);
+ concat_ws
+-----------
+ ABCDE222
+(1 row)
+
+
+select concat_ws(null,'ABCDE', 2, null, 22);
+ concat_ws
+-----------
+ 
+(1 row)
+

src/test/regress/sql/pg_compatibility.sql

@@ -13,4 +13,8 @@ select concat(null,'','','') is null;
 
 select concat('','') is null;
 
-select ''::int;
+select ''::int;
+
+select concat_ws('','ABCDE', 2, null, 22);
+
+select concat_ws(null,'ABCDE', 2, null, 22);