Avoiding a small risk of failure in timestamp(tz) regression tests

I noticed a buildfarm failure here:

https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=skate&dt=2019-12-22%2007%3A49%3A22

================== pgsql.build/src/test/regress/regression.diffs ==================
*** /home/pgbf/buildroot/REL_10_STABLE/pgsql.build/src/test/regress/expected/timestamptz.out    2019-12-13
08:51:47.000000000+0100 
--- /home/pgbf/buildroot/REL_10_STABLE/pgsql.build/src/test/regress/results/timestamptz.out    2019-12-22
09:00:00.000000000+0100 
***************
*** 27,33 ****
  SELECT count(*) AS One FROM TIMESTAMPTZ_TBL WHERE d1 = timestamp with time zone 'today';
   one
  -----
!    1
  (1 row)

  SELECT count(*) AS One FROM TIMESTAMPTZ_TBL WHERE d1 = timestamp with time zone 'tomorrow';
--- 27,33 ----
  SELECT count(*) AS One FROM TIMESTAMPTZ_TBL WHERE d1 = timestamp with time zone 'today';
   one
  -----
!    2
  (1 row)

  SELECT count(*) AS One FROM TIMESTAMPTZ_TBL WHERE d1 = timestamp with time zone 'tomorrow';


Judging by the reported timestamp on the results file, this is an instance
of the problem mentioned in the comments in timestamptz.sql:

-- NOTE: it is possible for this part of the test to fail if the transaction
-- block is entered exactly at local midnight; then 'now' and 'today' have
-- the same values and the counts will come out different.

On most machines it'd be pretty hard to hit that window; I speculate that
"skate" has got a very low-resolution system clock, making the window
larger.  Nonetheless, a test that's got designed-in failure modes is
annoying.  We can dodge this by separating the test for "now" from the
tests for the today/tomorrow/etc input strings, as attached.
Any objections?

            regards, tom lane

diff --git a/src/test/regress/expected/timestamp.out b/src/test/regress/expected/timestamp.out
index 39a4d49..5f97505 100644
--- a/src/test/regress/expected/timestamp.out
+++ b/src/test/regress/expected/timestamp.out
@@ -5,20 +5,9 @@ CREATE TABLE TIMESTAMP_TBL (d1 timestamp(2) without time zone);
 -- Test shorthand input values
 -- We can't just "select" the results since they aren't constants; test for
 -- equality instead.  We can do that by running the test inside a transaction
--- block, within which the value of 'now' shouldn't change.  We also check
--- that 'now' *does* change over a reasonable interval such as 100 msec.
--- NOTE: it is possible for this part of the test to fail if the transaction
--- block is entered exactly at local midnight; then 'now' and 'today' have
--- the same values and the counts will come out different.
-INSERT INTO TIMESTAMP_TBL VALUES ('now');
-SELECT pg_sleep(0.1);
- pg_sleep
-----------
-
-(1 row)
-
+-- block, within which the value of 'now' shouldn't change, and so these
+-- related values shouldn't either.
 BEGIN;
-INSERT INTO TIMESTAMP_TBL VALUES ('now');
 INSERT INTO TIMESTAMP_TBL VALUES ('today');
 INSERT INTO TIMESTAMP_TBL VALUES ('yesterday');
 INSERT INTO TIMESTAMP_TBL VALUES ('tomorrow');
@@ -43,15 +32,17 @@ SELECT count(*) AS One FROM TIMESTAMP_TBL WHERE d1 = timestamp without time zone
    1
 (1 row)

-SELECT count(*) AS One FROM TIMESTAMP_TBL WHERE d1 = timestamp(2) without time zone 'now';
- one
------
-   1
-(1 row)
-
 COMMIT;
 DELETE FROM TIMESTAMP_TBL;
--- verify uniform transaction time within transaction block
+-- Verify that 'now' *does* change over a reasonable interval such as 100 msec,
+-- and that it doesn't change over the same interval within a transaction block
+INSERT INTO TIMESTAMP_TBL VALUES ('now');
+SELECT pg_sleep(0.1);
+ pg_sleep
+----------
+
+(1 row)
+
 BEGIN;
 INSERT INTO TIMESTAMP_TBL VALUES ('now');
 SELECT pg_sleep(0.1);
@@ -73,6 +64,12 @@ SELECT count(*) AS two FROM TIMESTAMP_TBL WHERE d1 = timestamp(2) without time z
    2
 (1 row)

+SELECT count(d1) AS three, count(DISTINCT d1) AS two FROM TIMESTAMP_TBL;
+ three | two
+-------+-----
+     3 |   2
+(1 row)
+
 COMMIT;
 TRUNCATE TIMESTAMP_TBL;
 -- Special values
diff --git a/src/test/regress/expected/timestamptz.out b/src/test/regress/expected/timestamptz.out
index bb89910..639b503 100644
--- a/src/test/regress/expected/timestamptz.out
+++ b/src/test/regress/expected/timestamptz.out
@@ -5,20 +5,9 @@ CREATE TABLE TIMESTAMPTZ_TBL (d1 timestamp(2) with time zone);
 -- Test shorthand input values
 -- We can't just "select" the results since they aren't constants; test for
 -- equality instead.  We can do that by running the test inside a transaction
--- block, within which the value of 'now' shouldn't change.  We also check
--- that 'now' *does* change over a reasonable interval such as 100 msec.
--- NOTE: it is possible for this part of the test to fail if the transaction
--- block is entered exactly at local midnight; then 'now' and 'today' have
--- the same values and the counts will come out different.
-INSERT INTO TIMESTAMPTZ_TBL VALUES ('now');
-SELECT pg_sleep(0.1);
- pg_sleep
-----------
-
-(1 row)
-
+-- block, within which the value of 'now' shouldn't change, and so these
+-- related values shouldn't either.
 BEGIN;
-INSERT INTO TIMESTAMPTZ_TBL VALUES ('now');
 INSERT INTO TIMESTAMPTZ_TBL VALUES ('today');
 INSERT INTO TIMESTAMPTZ_TBL VALUES ('yesterday');
 INSERT INTO TIMESTAMPTZ_TBL VALUES ('tomorrow');
@@ -42,7 +31,13 @@ SELECT count(*) AS One FROM TIMESTAMPTZ_TBL WHERE d1 = timestamp with time zone
    1
 (1 row)

-SELECT count(*) AS One FROM TIMESTAMPTZ_TBL WHERE d1 = timestamp(2) with time zone 'now';
+SELECT count(*) AS One FROM TIMESTAMPTZ_TBL WHERE d1 = timestamp with time zone 'tomorrow EST';
+ one
+-----
+   1
+(1 row)
+
+SELECT count(*) AS One FROM TIMESTAMPTZ_TBL WHERE d1 = timestamp with time zone 'tomorrow zulu';
  one
 -----
    1
@@ -50,7 +45,15 @@ SELECT count(*) AS One FROM TIMESTAMPTZ_TBL WHERE d1 = timestamp(2) with time zo

 COMMIT;
 DELETE FROM TIMESTAMPTZ_TBL;
--- verify uniform transaction time within transaction block
+-- Verify that 'now' *does* change over a reasonable interval such as 100 msec,
+-- and that it doesn't change over the same interval within a transaction block
+INSERT INTO TIMESTAMPTZ_TBL VALUES ('now');
+SELECT pg_sleep(0.1);
+ pg_sleep
+----------
+
+(1 row)
+
 BEGIN;
 INSERT INTO TIMESTAMPTZ_TBL VALUES ('now');
 SELECT pg_sleep(0.1);
@@ -72,8 +75,14 @@ SELECT count(*) AS two FROM TIMESTAMPTZ_TBL WHERE d1 = timestamp(2) with time zo
    2
 (1 row)

+SELECT count(d1) AS three, count(DISTINCT d1) AS two FROM TIMESTAMPTZ_TBL;
+ three | two
+-------+-----
+     3 |   2
+(1 row)
+
 COMMIT;
-DELETE FROM TIMESTAMPTZ_TBL;
+TRUNCATE TIMESTAMPTZ_TBL;
 -- Special values
 INSERT INTO TIMESTAMPTZ_TBL VALUES ('-infinity');
 INSERT INTO TIMESTAMPTZ_TBL VALUES ('infinity');
diff --git a/src/test/regress/sql/timestamp.sql b/src/test/regress/sql/timestamp.sql
index 0d4d465..7b58c3c 100644
--- a/src/test/regress/sql/timestamp.sql
+++ b/src/test/regress/sql/timestamp.sql
@@ -7,18 +7,11 @@ CREATE TABLE TIMESTAMP_TBL (d1 timestamp(2) without time zone);
 -- Test shorthand input values
 -- We can't just "select" the results since they aren't constants; test for
 -- equality instead.  We can do that by running the test inside a transaction
--- block, within which the value of 'now' shouldn't change.  We also check
--- that 'now' *does* change over a reasonable interval such as 100 msec.
--- NOTE: it is possible for this part of the test to fail if the transaction
--- block is entered exactly at local midnight; then 'now' and 'today' have
--- the same values and the counts will come out different.
-
-INSERT INTO TIMESTAMP_TBL VALUES ('now');
-SELECT pg_sleep(0.1);
+-- block, within which the value of 'now' shouldn't change, and so these
+-- related values shouldn't either.

 BEGIN;

-INSERT INTO TIMESTAMP_TBL VALUES ('now');
 INSERT INTO TIMESTAMP_TBL VALUES ('today');
 INSERT INTO TIMESTAMP_TBL VALUES ('yesterday');
 INSERT INTO TIMESTAMP_TBL VALUES ('tomorrow');
@@ -29,19 +22,24 @@ INSERT INTO TIMESTAMP_TBL VALUES ('tomorrow zulu');
 SELECT count(*) AS One FROM TIMESTAMP_TBL WHERE d1 = timestamp without time zone 'today';
 SELECT count(*) AS Three FROM TIMESTAMP_TBL WHERE d1 = timestamp without time zone 'tomorrow';
 SELECT count(*) AS One FROM TIMESTAMP_TBL WHERE d1 = timestamp without time zone 'yesterday';
-SELECT count(*) AS One FROM TIMESTAMP_TBL WHERE d1 = timestamp(2) without time zone 'now';

 COMMIT;

 DELETE FROM TIMESTAMP_TBL;

--- verify uniform transaction time within transaction block
+-- Verify that 'now' *does* change over a reasonable interval such as 100 msec,
+-- and that it doesn't change over the same interval within a transaction block
+
+INSERT INTO TIMESTAMP_TBL VALUES ('now');
+SELECT pg_sleep(0.1);
+
 BEGIN;
 INSERT INTO TIMESTAMP_TBL VALUES ('now');
 SELECT pg_sleep(0.1);
 INSERT INTO TIMESTAMP_TBL VALUES ('now');
 SELECT pg_sleep(0.1);
 SELECT count(*) AS two FROM TIMESTAMP_TBL WHERE d1 = timestamp(2) without time zone 'now';
+SELECT count(d1) AS three, count(DISTINCT d1) AS two FROM TIMESTAMP_TBL;
 COMMIT;

 TRUNCATE TIMESTAMP_TBL;
diff --git a/src/test/regress/sql/timestamptz.sql b/src/test/regress/sql/timestamptz.sql
index 67b4a7d..300302d 100644
--- a/src/test/regress/sql/timestamptz.sql
+++ b/src/test/regress/sql/timestamptz.sql
@@ -7,18 +7,11 @@ CREATE TABLE TIMESTAMPTZ_TBL (d1 timestamp(2) with time zone);
 -- Test shorthand input values
 -- We can't just "select" the results since they aren't constants; test for
 -- equality instead.  We can do that by running the test inside a transaction
--- block, within which the value of 'now' shouldn't change.  We also check
--- that 'now' *does* change over a reasonable interval such as 100 msec.
--- NOTE: it is possible for this part of the test to fail if the transaction
--- block is entered exactly at local midnight; then 'now' and 'today' have
--- the same values and the counts will come out different.
-
-INSERT INTO TIMESTAMPTZ_TBL VALUES ('now');
-SELECT pg_sleep(0.1);
+-- block, within which the value of 'now' shouldn't change, and so these
+-- related values shouldn't either.

 BEGIN;

-INSERT INTO TIMESTAMPTZ_TBL VALUES ('now');
 INSERT INTO TIMESTAMPTZ_TBL VALUES ('today');
 INSERT INTO TIMESTAMPTZ_TBL VALUES ('yesterday');
 INSERT INTO TIMESTAMPTZ_TBL VALUES ('tomorrow');
@@ -28,22 +21,29 @@ INSERT INTO TIMESTAMPTZ_TBL VALUES ('tomorrow zulu');
 SELECT count(*) AS One FROM TIMESTAMPTZ_TBL WHERE d1 = timestamp with time zone 'today';
 SELECT count(*) AS One FROM TIMESTAMPTZ_TBL WHERE d1 = timestamp with time zone 'tomorrow';
 SELECT count(*) AS One FROM TIMESTAMPTZ_TBL WHERE d1 = timestamp with time zone 'yesterday';
-SELECT count(*) AS One FROM TIMESTAMPTZ_TBL WHERE d1 = timestamp(2) with time zone 'now';
+SELECT count(*) AS One FROM TIMESTAMPTZ_TBL WHERE d1 = timestamp with time zone 'tomorrow EST';
+SELECT count(*) AS One FROM TIMESTAMPTZ_TBL WHERE d1 = timestamp with time zone 'tomorrow zulu';

 COMMIT;

 DELETE FROM TIMESTAMPTZ_TBL;

--- verify uniform transaction time within transaction block
+-- Verify that 'now' *does* change over a reasonable interval such as 100 msec,
+-- and that it doesn't change over the same interval within a transaction block
+
+INSERT INTO TIMESTAMPTZ_TBL VALUES ('now');
+SELECT pg_sleep(0.1);
+
 BEGIN;
 INSERT INTO TIMESTAMPTZ_TBL VALUES ('now');
 SELECT pg_sleep(0.1);
 INSERT INTO TIMESTAMPTZ_TBL VALUES ('now');
 SELECT pg_sleep(0.1);
 SELECT count(*) AS two FROM TIMESTAMPTZ_TBL WHERE d1 = timestamp(2) with time zone 'now';
+SELECT count(d1) AS three, count(DISTINCT d1) AS two FROM TIMESTAMPTZ_TBL;
 COMMIT;

-DELETE FROM TIMESTAMPTZ_TBL;
+TRUNCATE TIMESTAMPTZ_TBL;

 -- Special values
 INSERT INTO TIMESTAMPTZ_TBL VALUES ('-infinity');