[Remote Store] Add missing unit test in main (opensearch-project#9101)

Signed-off-by: Suraj Singh <surajrider@gmail.com>
Signed-off-by: Ivan Brusic <ivan.brusic@flocksafety.com>

Author: dreamer-89

server/src/test/java/org/opensearch/index/store/RemoteSegmentStoreDirectoryTests.java

@@ -758,6 +758,35 @@ public void testUploadMetadataNonEmpty() throws IOException {
         }
     }
 
+    public void testUploadMetadataMissingSegment() throws IOException {
+        populateMetadata();
+        remoteSegmentStoreDirectory.init();
+
+        Directory storeDirectory = mock(Directory.class);
+        IndexOutput indexOutput = mock(IndexOutput.class);
+
+        String generation = RemoteStoreUtils.invertLong(segmentInfos.getGeneration());
+        long primaryTermLong = indexShard.getLatestReplicationCheckpoint().getPrimaryTerm();
+        String primaryTerm = RemoteStoreUtils.invertLong(primaryTermLong);
+        when(storeDirectory.createOutput(startsWith("metadata__" + primaryTerm + "__" + generation), eq(IOContext.DEFAULT))).thenReturn(
+            indexOutput
+        );
+
+        Collection<String> segmentFiles = List.of("_123.si");
+        assertThrows(
+            NoSuchFileException.class,
+            () -> remoteSegmentStoreDirectory.uploadMetadata(
+                segmentFiles,
+                segmentInfos,
+                storeDirectory,
+                12L,
+                indexShard.getLatestReplicationCheckpoint()
+            )
+        );
+        verify(indexOutput).close();
+        verify(storeDirectory).deleteFile(startsWith("metadata__" + primaryTerm + "__" + generation));
+    }
+
     public void testUploadMetadataNoSegmentCommitInfos() throws IOException {
         SegmentInfos segInfos = indexShard.store().readLastCommittedSegmentsInfo();
         int numSegCommitInfos = segInfos.size();