flaky test fix

Signed-off-by: bowenlan-amzn <bowenlan23@gmail.com>

Author: bowenlan-amzn

src/test/kotlin/org/opensearch/indexmanagement/indexstatemanagement/action/RollupActionIT.kt

@@ -659,24 +659,32 @@ class RollupActionIT : IndexStateManagementRestTestCase() {
             )
 
         createPolicy(tier1Policy, tier1PolicyID)
-        createIndex(tier1IndexName, tier1PolicyID, mapping = sourceIndexMappingString)
+        // Create index WITHOUT policy first to avoid race condition where ISM starts
+        // rollup before data is indexed
+        createIndex(tier1IndexName, policyID = null, mapping = sourceIndexMappingString)
 
         // Insert test data with varying timestamps and categories
         val bulkRequest = StringBuilder()
         for (i in 1..100) {
-            val timestamp = "2024-01-01T${String.format("%02d", i % 24)}:00:00Z"
+            // Use Locale.ROOT to ensure ASCII digits regardless of test locale
+            val timestamp = "2024-01-01T${String.format(Locale.ROOT, "%02d", i % 24)}:00:00Z"
             val category = if (i % 2 == 0) "electronics" else "books"
             val userId = "user_${(i - 1) / 10 + 1}" // Creates user_1 to user_10
             val value = i * 10.0
             bulkRequest.append("""{"index":{"_index":"$tier1IndexName"}}""").append("\n")
             bulkRequest.append("""{"timestamp":"$timestamp","category":"$category","user_id":"$userId","value":$value}""").append("\n")
         }
-        client().makeRequest(
+        val bulkResponse = client().makeRequest(
             "POST",
             "/_bulk?refresh=true",
             emptyMap(),
             StringEntity(bulkRequest.toString(), ContentType.APPLICATION_JSON),
         )
+        val bulkResponseMap = bulkResponse.asMap()
+        assertFalse("Bulk request should not have errors: $bulkResponseMap", bulkResponseMap["errors"] as Boolean)
+
+        // Now add policy after data is indexed to ensure rollup sees all data
+        addPolicyToIndex(tier1IndexName, tier1PolicyID)
 
         // Execute Tier-1 rollup
         assertIndexRolledUp(tier1IndexName, tier1PolicyID, tier1Rollup)