Fixed error with rounded file creation time.

Author: rzharkov

src/test/isolation/expected/snapfs_get_snapshot_timestamp.out

@@ -4,11 +4,17 @@ starting permutation: s1_mk_sn
 step s1_mk_sn: 
 	select 1 as "make_snapshot" from pg_make_snapshot();
 	create table foo as select 'test_data';
-	select ( now() - ( select pg_get_snapshot_timestamp( ( select recent_snapshot from pg_control_snapshot() ) ) ) ) between '0 sec'::interval and '1 min'::interval as "timestamp_check"
+  select (
+		case
+			when ( ( date_trunc( 'second', now() ) - ( select pg_get_snapshot_timestamp( ( select recent_snapshot from pg_control_snapshot() ) ) ) ) between '-1 sec'::interval and '3 sec'::interval )
+			then 'passed'
+			else 'Now:' || date_trunc( 'second', now() )::varchar || ' SN:' || ( select pg_get_snapshot_timestamp( ( select recent_snapshot from pg_control_snapshot() ) ) )
+			end
+	) as "timestamp_check"
 
 make_snapshot  
 
 1              
 timestamp_check
 
-t              
+passed         

src/test/isolation/specs/snapfs_get_snapshot_timestamp.spec

@@ -1,4 +1,4 @@
-# The recent just created snapshot cannot be older than 1 minute :)
+# The recent just created snapshot cannot be older than 3 seconds
 
 teardown {
 	select pg_remove_snapshot( ( select recent_snapshot from pg_control_snapshot() ) );
@@ -9,7 +9,13 @@ session "s1"
 step "s1_mk_sn" {
 	select 1 as "make_snapshot" from pg_make_snapshot();
 	create table foo as select 'test_data';
-	select ( now() - ( select pg_get_snapshot_timestamp( ( select recent_snapshot from pg_control_snapshot() ) ) ) ) between '0 sec'::interval and '1 min'::interval as "timestamp_check"
+  select (
+		case
+			when ( ( date_trunc( 'second', now() ) - ( select pg_get_snapshot_timestamp( ( select recent_snapshot from pg_control_snapshot() ) ) ) ) between '-1 sec'::interval and '3 sec'::interval )
+			then 'passed'
+			else 'Now:' || date_trunc( 'second', now() )::varchar || ' SN:' || ( select pg_get_snapshot_timestamp( ( select recent_snapshot from pg_control_snapshot() ) ) )
+			end
+	) as "timestamp_check"
 }
 
 permutation "s1_mk_sn"