allocation: fix up random long usage with inclusive bound (elastic#139163)

In the write load constraint monitor tests, the criteria for specifying a
non-hotspot node generated a random queue latency between 0 and the hotspot
threshold setting. In usage, the random number generation used the threshold as
an inclusive bound, while it needed to be an exclusive bound. This became an
issue recently, with the addition of tests that specify a certain number of
hotspot nodes, and remove them individually throughout the test
(testHotspotCountTurnsOff).

Fixes: elastic#139161

Author: schase-es

muted-tests.yml

@@ -503,9 +503,6 @@ tests:
 - class: org.elasticsearch.xpack.logsdb.RandomizedRollingUpgradeIT
   method: testIndexingStandardSource
   issue: https://github.com/elastic/elasticsearch/issues/139153
-- class: org.elasticsearch.cluster.routing.allocation.WriteLoadConstraintMonitorTests
-  method: testHotspotCountTurnsOff
-  issue: https://github.com/elastic/elasticsearch/issues/139161
 
 # Examples:
 #

server/src/test/java/org/elasticsearch/cluster/routing/allocation/WriteLoadConstraintMonitorTests.java

@@ -660,6 +660,7 @@ private static ClusterInfo createClusterInfoWithHotSpots(
         long queueLatencyThresholdMillis,
         int highUtilizationThresholdPercent
     ) {
+        assert queueLatencyThresholdMillis > 0 : "queue latency threshold must be positive";
         final Set<String> hotspotNodesSet = new HashSet<>(hotspotNodes);
         final float maxRatioForUnderUtilised = (highUtilizationThresholdPercent - 1) / 100.0f;
         ClusterInfo clusterInfo = ClusterInfo.builder()
@@ -690,7 +691,7 @@ private static ClusterInfo createClusterInfoWithHotSpots(
                             new NodeUsageStatsForThreadPools.ThreadPoolUsageStats(
                                 randomNonNegativeInt(),
                                 randomFloatBetween(0f, maxRatioForUnderUtilised, true),
-                                randomLongBetween(0, queueLatencyThresholdMillis)
+                                randomLongBetween(0, queueLatencyThresholdMillis - 1)
                             )
                         )
                     );