Expand tests for factorial

Move from int4 to numeric test.  (They were originally int4 functions,
but were reimplemented for numeric in
04a4821a.)  Add some tests for edge
cases.

Discussion: https://www.postgresql.org/message-id/flat/6ce1df0e-86a3-e544-743a-f357ff663f68%402ndquadrant.com

src/test/regress/expected/int4.out

@@ -299,18 +299,6 @@ SELECT int4 '1000' < int4 '999' AS false;
  f
 (1 row)
 
-SELECT 4! AS twenty_four;
- twenty_four 
--------------
-          24
-(1 row)
-
-SELECT !!3 AS six;
- six 
------
-   6
-(1 row)
-
 SELECT 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 AS ten;
  ten 
 -----

src/test/regress/expected/numeric.out

@@ -2315,3 +2315,44 @@ FROM (VALUES (0::numeric, 0::numeric),
 
 SELECT lcm(9999 * (10::numeric)^131068 + (10::numeric^131068 - 1), 2); -- overflow
 ERROR:  value overflows numeric format
+--
+-- Tests for factorial
+--
+SELECT 4!;
+ ?column? 
+----------
+       24
+(1 row)
+
+SELECT !!3;
+ ?column? 
+----------
+        6
+(1 row)
+
+SELECT factorial(15);
+   factorial   
+---------------
+ 1307674368000
+(1 row)
+
+SELECT 100000!;
+ERROR:  value overflows numeric format
+SELECT 0!;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT -4!;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT factorial(-4);
+ factorial 
+-----------
+         1
+(1 row)
+

src/test/regress/sql/int4.sql

@@ -114,10 +114,6 @@ SELECT int2 '2' * int4 '2' = int4 '16' / int2 '4' AS true;
 
 SELECT int4 '1000' < int4 '999' AS false;
 
-SELECT 4! AS twenty_four;
-
-SELECT !!3 AS six;
-
 SELECT 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 AS ten;
 
 SELECT 2 + 2 / 2 AS three;

src/test/regress/sql/numeric.sql

@@ -1111,3 +1111,14 @@ FROM (VALUES (0::numeric, 0::numeric),
              (4232.820::numeric, 132.72000::numeric)) AS v(a, b);
 
 SELECT lcm(9999 * (10::numeric)^131068 + (10::numeric^131068 - 1), 2); -- overflow
+
+--
+-- Tests for factorial
+--
+SELECT 4!;
+SELECT !!3;
+SELECT factorial(15);
+SELECT 100000!;
+SELECT 0!;
+SELECT -4!;
+SELECT factorial(-4);