Fix for flaky test IndexServiceTests.testAsyncTranslogTrimTaskOnClosedIndex (opensearch-project#11337)

Signed-off-by: Ankit Kala <ankikala@amazon.com>

Author: ankitkala

server/src/test/java/org/opensearch/index/IndexServiceTests.java

@@ -452,12 +452,7 @@ public void testAsyncTranslogTrimTaskOnClosedIndex() throws Exception {
         assertTrue(indexService.getTrimTranslogTask().mustReschedule());
 
         final Engine readOnlyEngine = getEngine(indexService.getShard(0));
-        assertBusy(
-            () -> assertThat(
-                readOnlyEngine.translogManager().getTranslogStats().getTranslogSizeInBytes(),
-                equalTo((long) Translog.DEFAULT_HEADER_SIZE_IN_BYTES)
-            )
-        );
+        assertBusy(() -> assertTrue(isTranslogEmpty(readOnlyEngine)));
 
         assertAcked(client().admin().indices().prepareOpen("test").setWaitForActiveShards(ActiveShardCount.DEFAULT));
 
@@ -467,6 +462,12 @@ public void testAsyncTranslogTrimTaskOnClosedIndex() throws Exception {
         assertThat(translog.stats().estimatedNumberOfOperations(), equalTo(0));
     }
 
+    boolean isTranslogEmpty(Engine engine) {
+        long tlogSize = engine.translogManager().getTranslogStats().getTranslogSizeInBytes();
+        // translog contains 1(or 2 in some corner cases) empty readers.
+        return tlogSize == Translog.DEFAULT_HEADER_SIZE_IN_BYTES || tlogSize == 2 * Translog.DEFAULT_HEADER_SIZE_IN_BYTES;
+    }
+
     public void testIllegalFsyncInterval() {
         Settings settings = Settings.builder()
             .put(IndexSettings.INDEX_TRANSLOG_SYNC_INTERVAL_SETTING.getKey(), "0ms") // disable