Add tests

Signed-off-by: Aleksandr Tuliakov <tulyakov@yandex-team.ru>

Author: MrChaos1993

server/src/main/java/org/apache/lucene/codecs/lucene90/Lucene90StoredFieldsFormatComparator.java

@@ -11,7 +11,9 @@
 /**
  * This class is a custom comparator for Lucene90StoredFieldsFormat
  */
-public class Lucene90StoredFieldsFormatComparator {
+public final class Lucene90StoredFieldsFormatComparator {
+    private Lucene90StoredFieldsFormatComparator() {}
+
     public static boolean equal(Lucene90StoredFieldsFormat one, Lucene90StoredFieldsFormat two) {
         return one.mode == two.mode;
     }

server/src/main/java/org/opensearch/index/shard/OpenSearchMergePolicy.java

@@ -87,21 +87,24 @@ public MergePolicy getDelegate() {
         return in;
     }
 
-    private boolean shouldUpgrade(SegmentCommitInfo info) {
+    boolean shouldUpgrade(SegmentCommitInfo info) {
         org.apache.lucene.util.Version old = info.info.getVersion();
         org.apache.lucene.util.Version cur = Version.CURRENT.luceneVersion;
 
         // Something seriously wrong if this trips:
-        assert old.major <= cur.major;
+        assert cur.major >= old.major;
 
         if (cur.major > old.major) {
             // Always upgrade segment if Lucene's major version is too old
             return true;
         }
 
-        if (upgradeOnlyAncientSegments == false && cur.minor > old.minor) {
-            // If it's only a minor version difference, and we are not upgrading only ancient segments,
-            // also upgrade:
+        if (upgradeOnlyAncientSegments) {
+            // Skip other checks, because we already check major versions and we are upgrading only ancient segments
+            return false;
+        }
+
+        if (cur.minor > old.minor) {
             return true;
         }
 

server/src/test/java/org/opensearch/index/shard/OpenSearchMergePolicyTests.java

@@ -0,0 +1,110 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.index.shard;
+
+import org.apache.lucene.backward_codecs.lucene100.Lucene100Codec;
+import org.apache.lucene.backward_codecs.lucene912.Lucene912Codec;
+import org.apache.lucene.codecs.Codec;
+import org.apache.lucene.codecs.lucene101.Lucene101Codec;
+import org.apache.lucene.codecs.lucene90.Lucene90StoredFieldsFormat;
+import org.apache.lucene.codecs.lucene90.Lucene90StoredFieldsFormatComparator;
+import org.apache.lucene.index.MergePolicy;
+import org.apache.lucene.index.SegmentCommitInfo;
+import org.apache.lucene.index.SegmentInfo;
+import org.apache.lucene.store.Directory;
+import org.apache.lucene.util.Version;
+import org.opensearch.index.codec.composite.composite101.Composite101Codec;
+import org.opensearch.test.OpenSearchTestCase;
+
+import java.util.Map;
+
+import org.mockito.Mockito;
+
+import static org.apache.lucene.codecs.lucene90.Lucene90StoredFieldsFormat.Mode.BEST_COMPRESSION;
+import static org.apache.lucene.codecs.lucene90.Lucene90StoredFieldsFormat.Mode.BEST_SPEED;
+
+/**
+ * Very simple checks for {@link OpenSearchMergePolicy}
+ */
+public class OpenSearchMergePolicyTests extends OpenSearchTestCase {
+    public void testShouldUpgrade() {
+        var mockMergePolicy = Mockito.mock(MergePolicy.class);
+        var openSearchMergePolicy = new OpenSearchMergePolicy(mockMergePolicy, new Lucene101Codec());
+        assertFalse(openSearchMergePolicy.shouldUpgrade(createSegmentCommitInfo(Version.LATEST, new Lucene101Codec())));
+        assertTrue(openSearchMergePolicy.shouldUpgrade(createSegmentCommitInfo(Version.LUCENE_10_2_0, new Lucene100Codec())));
+        assertTrue(
+            openSearchMergePolicy.shouldUpgrade(
+                createSegmentCommitInfo(Version.LATEST, new Lucene101Codec(Lucene101Codec.Mode.BEST_COMPRESSION))
+            )
+        );
+        assertTrue(openSearchMergePolicy.shouldUpgrade(createSegmentCommitInfo(Version.LUCENE_9_12_2, new Lucene912Codec())));
+        assertTrue(openSearchMergePolicy.shouldUpgrade(createSegmentCommitInfo(Version.LATEST, new Composite101Codec())));
+
+        openSearchMergePolicy.setUpgradeInProgress(true, true);
+        assertTrue(openSearchMergePolicy.shouldUpgrade(createSegmentCommitInfo(Version.LUCENE_9_12_2, new Lucene912Codec())));
+        assertFalse(openSearchMergePolicy.shouldUpgrade(createSegmentCommitInfo(Version.LUCENE_10_0_0, new Lucene100Codec())));
+    }
+
+    /**
+     * Very simple equal checks for {@link Lucene90StoredFieldsFormatComparator}
+     */
+    public void testLucene90StoredFieldsFormatComparatorEqual() {
+        assertTrue(Lucene90StoredFieldsFormatComparator.equal(new Lucene90StoredFieldsFormat(), new Lucene90StoredFieldsFormat()));
+        assertTrue(
+            Lucene90StoredFieldsFormatComparator.equal(new Lucene90StoredFieldsFormat(), new Lucene90StoredFieldsFormat(BEST_SPEED))
+        );
+        assertTrue(
+            Lucene90StoredFieldsFormatComparator.equal(
+                new Lucene90StoredFieldsFormat(BEST_SPEED),
+                new Lucene90StoredFieldsFormat(BEST_SPEED)
+            )
+        );
+        assertTrue(
+            Lucene90StoredFieldsFormatComparator.equal(
+                new Lucene90StoredFieldsFormat(BEST_COMPRESSION),
+                new Lucene90StoredFieldsFormat(BEST_COMPRESSION)
+            )
+        );
+        assertFalse(
+            Lucene90StoredFieldsFormatComparator.equal(new Lucene90StoredFieldsFormat(), new Lucene90StoredFieldsFormat(BEST_COMPRESSION))
+        );
+        assertFalse(
+            Lucene90StoredFieldsFormatComparator.equal(
+                new Lucene90StoredFieldsFormat(BEST_SPEED),
+                new Lucene90StoredFieldsFormat(BEST_COMPRESSION)
+            )
+        );
+        assertFalse(
+            Lucene90StoredFieldsFormatComparator.equal(
+                new Lucene90StoredFieldsFormat(BEST_COMPRESSION),
+                new Lucene90StoredFieldsFormat(BEST_SPEED)
+            )
+        );
+    }
+
+    private SegmentCommitInfo createSegmentCommitInfo(Version version, Codec codec) {
+        var id = new byte[16];
+        var mockDir = Mockito.mock(Directory.class);
+        var segmentInfo = new SegmentInfo(
+            mockDir,
+            version,
+            version,
+            "",
+            Integer.MAX_VALUE,
+            false,
+            false,
+            codec,
+            Map.of(),
+            id,
+            Map.of(),
+            null
+        );
+        return new SegmentCommitInfo(segmentInfo, 0, 0, 0, 0, 0, id);
+    }
+}