Fix translog stats in testPrepareIndexForPeerRecovery (#46137)

When recovering a shard locally, we use a translog snapshot from
newSnapshotFromGen which consists of all readers from a certain
generation. In the test, we use newSnapshotFromMinSeqNo for the
expectation. The snapshot of this method includes only readers
containing operations in the requesting range.

Closes #46022

server/src/test/java/org/elasticsearch/indices/recovery/PeerRecoveryTargetServiceTests.java

@@ -35,6 +35,7 @@ import org.elasticsearch.common.UUIDs;
 import org.elasticsearch.common.bytes.BytesArray;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.xcontent.XContentType;
+import org.elasticsearch.index.engine.Engine;
 import org.elasticsearch.index.engine.NoOpEngine;
 import org.elasticsearch.index.mapper.SourceToParse;
 import org.elasticsearch.index.seqno.SeqNoStats;
@@ -173,8 +174,14 @@ public class PeerRecoveryTargetServiceTests extends IndexShardTestCase {
         long globalCheckpoint = populateRandomData(shard).getGlobalCheckpoint();
         Optional<SequenceNumbers.CommitInfo> safeCommit = shard.store().findSafeIndexCommit(globalCheckpoint);
         assertTrue(safeCommit.isPresent());
+        final Translog.TranslogGeneration recoveringTranslogGeneration;
+        try (Engine.IndexCommitRef commitRef = shard.acquireSafeIndexCommit()) {
+            recoveringTranslogGeneration = new Translog.TranslogGeneration(
+                commitRef.getIndexCommit().getUserData().get(Translog.TRANSLOG_UUID_KEY),
+                Long.parseLong(commitRef.getIndexCommit().getUserData().get(Translog.TRANSLOG_GENERATION_KEY)));
+        }
         int expectedTotalLocal = 0;
-        try (Translog.Snapshot snapshot = getTranslog(shard).newSnapshotFromMinSeqNo(safeCommit.get().localCheckpoint + 1)) {
+        try (Translog.Snapshot snapshot = getTranslog(shard).newSnapshotFromGen(recoveringTranslogGeneration, globalCheckpoint)) {
             Translog.Operation op;
             while ((op = snapshot.next()) != null) {
                 if (op.seqNo() <= globalCheckpoint) {