Relax translog assertion in testRestoreLocalHistoryFromTranslog (#45943)

Since #45473, we trim translog below the local checkpoint of the safe
commit immediately if soft-deletes enabled. In
testRestoreLocalHistoryFromTranslog, we should have a safe commit after
recoverFromTranslog is called; then we will trim translog files which
contain only operations that are at most the global checkpoint.

With this change, we relax the assertion to ensure that we don't put
operations to translog while recovering history from the local translog.

server/src/test/java/org/elasticsearch/index/engine/InternalEngineTests.java

@@ -4515,7 +4515,6 @@ public class InternalEngineTests extends EngineTestCase {
             final EngineConfig engineConfig;
             final SeqNoStats prevSeqNoStats;
             final List<DocIdSeqNoAndSource> prevDocs;
-            final int totalTranslogOps;
             try (InternalEngine engine = createEngine(store, createTempDir(), globalCheckpoint::get)) {
                 engineConfig = engine.config();
                 for (final long seqNo : seqNos) {
@@ -4534,16 +4533,19 @@ public class InternalEngineTests extends EngineTestCase {
                 engine.syncTranslog();
                 prevSeqNoStats = engine.getSeqNoStats(globalCheckpoint.get());
                 prevDocs = getDocIds(engine, true);
-                totalTranslogOps = engine.getTranslog().totalOperations();
             }
             try (InternalEngine engine = new InternalEngine(engineConfig)) {
+                final Translog.TranslogGeneration currrentTranslogGeneration = new Translog.TranslogGeneration(
+                    engine.getTranslog().getTranslogUUID(), engine.getTranslog().currentFileGeneration());
                 engine.recoverFromTranslog(translogHandler, globalCheckpoint.get());
                 engine.restoreLocalHistoryFromTranslog(translogHandler);
                 assertThat(getDocIds(engine, true), equalTo(prevDocs));
                 SeqNoStats seqNoStats = engine.getSeqNoStats(globalCheckpoint.get());
                 assertThat(seqNoStats.getLocalCheckpoint(), equalTo(prevSeqNoStats.getLocalCheckpoint()));
                 assertThat(seqNoStats.getMaxSeqNo(), equalTo(prevSeqNoStats.getMaxSeqNo()));
-                assertThat(engine.getTranslog().totalOperations(), equalTo(totalTranslogOps));
+                try (Translog.Snapshot snapshot = engine.getTranslog().newSnapshotFromGen(currrentTranslogGeneration, Long.MAX_VALUE)) {
+                    assertThat("restore from local translog must not add operations to translog", snapshot, SnapshotMatchers.size(0));
+                }
             }
             assertConsistentHistoryBetweenTranslogAndLuceneIndex(engine, createMapperService("test"));
         }