Improve tests of date_trunc() with infinity and unsupported units

Commit d85ce012f99f has added some new error handling code to
date_trunc() of timestamp, timestamptz, and interval with infinite
values.

However, the new test cases added by that commit did not actually test
all of the new code, missing coverage for the following cases:
1) For timestamp without time zone:
1-1) infinite value with valid unit
1-2) infinite value with unsupported unit
1-3) finite value with unsupported unit, for a code path older than
d85ce012f99f.
2) For timestamp with time zone, without a time zone specified for the
truncation:
2-1) infinite value with valid unit
2-2) infinite value with unsupported unit
2-3) finite value with unsupported unit, for a code path older than
d85ce012f99f.
3) For timestamp with time zone, with a time zone specified for the
truncation:
3-1) infinite value with valid unit.
3-2) infinite value with unsupported unit.

This commit also provides coverage for the bug fixed in 2242b26ce472,
through cases 2-1) and 3-1), when using an infinite value with a valid
unit, with[out] the optional time zone parameter used for the
truncation.

Author: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://postgr.es/m/2d320b6f-b4af-4fbc-9eec-5d0fa15d187b@eisentraut.org
Discussion: https://postgr.es/m/4bf60a84-2862-4a53-acd5-8eddf134a60e@eisentraut.org
Backpatch-through: 18

src/test/regress/expected/timestamp.out

@@ -591,6 +591,16 @@ SELECT date_trunc( 'week', timestamp '2004-02-29 15:44:17.71393' ) AS week_trunc
  Mon Feb 23 00:00:00 2004
 (1 row)
 
+SELECT date_trunc( 'week', timestamp 'infinity' ) AS inf_trunc;
+ inf_trunc 
+-----------
+ infinity
+(1 row)
+
+SELECT date_trunc( 'timezone', timestamp '2004-02-29 15:44:17.71393' ) AS notsupp_trunc;
+ERROR:  unit "timezone" not supported for type timestamp without time zone
+SELECT date_trunc( 'timezone', timestamp 'infinity' ) AS notsupp_inf_trunc;
+ERROR:  unit "timezone" not supported for type timestamp without time zone
 SELECT date_trunc( 'ago', timestamp 'infinity' ) AS invalid_trunc;
 ERROR:  unit "ago" not recognized for type timestamp without time zone
 -- verify date_bin behaves the same as date_trunc for relevant intervals

src/test/regress/expected/timestamptz.out

@@ -760,6 +760,16 @@ SELECT date_trunc( 'week', timestamp with time zone '2004-02-29 15:44:17.71393'
  Mon Feb 23 00:00:00 2004 PST
 (1 row)
 
+SELECT date_trunc( 'week', timestamp with time zone 'infinity' ) AS inf_trunc;
+ inf_trunc 
+-----------
+ infinity
+(1 row)
+
+SELECT date_trunc( 'timezone', timestamp with time zone '2004-02-29 15:44:17.71393' ) AS notsupp_trunc;
+ERROR:  unit "timezone" not supported for type timestamp with time zone
+SELECT date_trunc( 'timezone', timestamp with time zone 'infinity' ) AS notsupp_inf_trunc;
+ERROR:  unit "timezone" not supported for type timestamp with time zone
 SELECT date_trunc( 'ago', timestamp with time zone 'infinity' ) AS invalid_trunc;
 ERROR:  unit "ago" not recognized for type timestamp with time zone
 SELECT date_trunc('day', timestamp with time zone '2001-02-16 20:38:40+00', 'Australia/Sydney') as sydney_trunc;  -- zone name
@@ -780,6 +790,14 @@ SELECT date_trunc('day', timestamp with time zone '2001-02-16 20:38:40+00', 'VET
  Thu Feb 15 20:00:00 2001 PST
 (1 row)
 
+SELECT date_trunc('timezone', timestamp with time zone 'infinity', 'GMT') AS notsupp_zone_trunc;
+ERROR:  unit "timezone" not supported for type timestamp with time zone
+SELECT date_trunc( 'week', timestamp with time zone 'infinity', 'GMT') AS inf_zone_trunc;
+ inf_zone_trunc 
+----------------
+ infinity
+(1 row)
+
 SELECT date_trunc('ago', timestamp with time zone 'infinity', 'GMT') AS invalid_zone_trunc;
 ERROR:  unit "ago" not recognized for type timestamp with time zone
 -- verify date_bin behaves the same as date_trunc for relevant intervals

src/test/regress/sql/timestamp.sql

@@ -175,7 +175,9 @@ SELECT d1 - timestamp without time zone '1997-01-02' AS diff
    FROM TIMESTAMP_TBL WHERE d1 BETWEEN '1902-01-01' AND '2038-01-01';
 
 SELECT date_trunc( 'week', timestamp '2004-02-29 15:44:17.71393' ) AS week_trunc;
-
+SELECT date_trunc( 'week', timestamp 'infinity' ) AS inf_trunc;
+SELECT date_trunc( 'timezone', timestamp '2004-02-29 15:44:17.71393' ) AS notsupp_trunc;
+SELECT date_trunc( 'timezone', timestamp 'infinity' ) AS notsupp_inf_trunc;
 SELECT date_trunc( 'ago', timestamp 'infinity' ) AS invalid_trunc;
 
 -- verify date_bin behaves the same as date_trunc for relevant intervals

src/test/regress/sql/timestamptz.sql

@@ -217,15 +217,18 @@ SELECT d1 - timestamp with time zone '1997-01-02' AS diff
    FROM TIMESTAMPTZ_TBL WHERE d1 BETWEEN '1902-01-01' AND '2038-01-01';
 
 SELECT date_trunc( 'week', timestamp with time zone '2004-02-29 15:44:17.71393' ) AS week_trunc;
+SELECT date_trunc( 'week', timestamp with time zone 'infinity' ) AS inf_trunc;
+SELECT date_trunc( 'timezone', timestamp with time zone '2004-02-29 15:44:17.71393' ) AS notsupp_trunc;
+SELECT date_trunc( 'timezone', timestamp with time zone 'infinity' ) AS notsupp_inf_trunc;
 SELECT date_trunc( 'ago', timestamp with time zone 'infinity' ) AS invalid_trunc;
 
 SELECT date_trunc('day', timestamp with time zone '2001-02-16 20:38:40+00', 'Australia/Sydney') as sydney_trunc;  -- zone name
 SELECT date_trunc('day', timestamp with time zone '2001-02-16 20:38:40+00', 'GMT') as gmt_trunc;  -- fixed-offset abbreviation
 SELECT date_trunc('day', timestamp with time zone '2001-02-16 20:38:40+00', 'VET') as vet_trunc;  -- variable-offset abbreviation
+SELECT date_trunc('timezone', timestamp with time zone 'infinity', 'GMT') AS notsupp_zone_trunc;
+SELECT date_trunc( 'week', timestamp with time zone 'infinity', 'GMT') AS inf_zone_trunc;
 SELECT date_trunc('ago', timestamp with time zone 'infinity', 'GMT') AS invalid_zone_trunc;
 
-
-
 -- verify date_bin behaves the same as date_trunc for relevant intervals
 SELECT
   str,