Fix the flaky test in clock.sql

src/test/regress/expected/clock.out

@@ -252,11 +252,12 @@ DETAIL:  Key (cc)=((100,100)) already exists.
 --
 SELECT (extract(epoch from now()) * 1000)::bigint AS epoch,
 	citus_get_node_clock() AS latest_clock \gset
--- Returns true
+-- Returns difference in epoch-milliseconds
-SELECT ABS(:epoch - cluster_clock_logical(:'latest_clock')) < 25;
+SELECT CASE WHEN msdiff BETWEEN 0 AND 25 THEN 0 ELSE msdiff END
- ?column?
+FROM ABS(:epoch - cluster_clock_logical(:'latest_clock')) msdiff;
+ msdiff
 ---------------------------------------------------------------------
- t
+      0
 (1 row)
 
 BEGIN;

src/test/regress/multi_schedule

@@ -81,7 +81,7 @@ test: multi_reference_table multi_select_for_update relation_access_tracking pg1
 test: custom_aggregate_support aggregate_support tdigest_aggregate_support
 test: multi_average_expression multi_working_columns multi_having_pushdown having_subquery
 test: multi_array_agg multi_limit_clause multi_orderby_limit_pushdown
-test: multi_jsonb_agg multi_jsonb_object_agg multi_json_agg multi_json_object_agg bool_agg ch_bench_having chbenchmark_all_queries expression_reference_join anonymous_columns clock
+test: multi_jsonb_agg multi_jsonb_object_agg multi_json_agg multi_json_object_agg bool_agg ch_bench_having chbenchmark_all_queries expression_reference_join anonymous_columns
 test: ch_bench_subquery_repartition
 test: multi_agg_type_conversion multi_count_type_conversion recursive_relation_planning_restriction_pushdown
 test: multi_partition_pruning single_hash_repartition_join unsupported_lateral_subqueries
@@ -101,6 +101,8 @@ test: undistribute_table
 test: run_command_on_all_nodes
 test: background_task_queue_monitor
 
+# Causal clock test
+test: clock
 
 # ---------
 # test that no tests leaked intermediate results. This should always be last

src/test/regress/sql/clock.sql

@@ -98,8 +98,9 @@ INSERT INTO cluster_clock_type values('(100, 100)');
 SELECT (extract(epoch from now()) * 1000)::bigint AS epoch,
 	citus_get_node_clock() AS latest_clock \gset
 
--- Returns true
+-- Returns difference in epoch-milliseconds
-SELECT ABS(:epoch - cluster_clock_logical(:'latest_clock')) < 25;
+SELECT CASE WHEN msdiff BETWEEN 0 AND 25 THEN 0 ELSE msdiff END
+FROM ABS(:epoch - cluster_clock_logical(:'latest_clock')) msdiff;
 
 BEGIN;
 SELECT citus_get_transaction_clock();