[FAB-17188] unit test for couchDB revision fetching functions

Add unit test for the following two functions
defined in statecouchdb package.

    addRevisionFromCache()
    addRevisionFromDB()

Signed-off-by: senthil <cendhu@gmail.com>

core/ledger/kvledger/txmgmt/statedb/statecouchdb/statecouchdb_test.go

@@ -1235,3 +1235,77 @@ func TestLoadCommittedVersion(t *testing.T) {
 	require.Equal(t, version.NewHeight(1, 4), ver)
 	require.True(t, ok)
 }
+
+func TestMissingRevisionRetrievalFromDB(t *testing.T) {
+	env := NewTestVDBEnv(t)
+	defer env.Cleanup()
+	chainID := "testmissingrevisionfromdb"
+	db, err := env.DBProvider.GetDBHandle(chainID)
+	require.NoError(t, err)
+
+	// store key1, key2, key3 to the DB
+	batch := statedb.NewUpdateBatch()
+	vv1 := statedb.VersionedValue{Value: []byte("value1"), Version: version.NewHeight(1, 1)}
+	vv2 := statedb.VersionedValue{Value: []byte("value2"), Version: version.NewHeight(1, 2)}
+	vv3 := statedb.VersionedValue{Value: []byte("value3"), Version: version.NewHeight(1, 3)}
+	batch.Put("ns1", "key1", vv1.Value, vv1.Version)
+	batch.Put("ns1", "key2", vv2.Value, vv2.Version)
+	batch.Put("ns1", "key3", vv3.Value, vv3.Version)
+	savePoint := version.NewHeight(2, 5)
+	db.ApplyUpdates(batch, savePoint)
+
+	// retrieve the versions of key1, key2, and key3
+	revisions := make(map[string]string)
+	require.NoError(t, db.(*VersionedDB).addMissingRevisionsFromDB("ns1", []string{"key1", "key2", "key3"}, revisions))
+	require.Equal(t, 3, len(revisions))
+
+	// update key1 and key2 but not key3
+	batch = statedb.NewUpdateBatch()
+	vv4 := statedb.VersionedValue{Value: []byte("value1"), Version: version.NewHeight(1, 1)}
+	vv5 := statedb.VersionedValue{Value: []byte("value2"), Version: version.NewHeight(1, 2)}
+	batch.Put("ns1", "key1", vv4.Value, vv4.Version)
+	batch.Put("ns1", "key2", vv5.Value, vv5.Version)
+	savePoint = version.NewHeight(3, 5)
+	db.ApplyUpdates(batch, savePoint)
+
+	// for key3, the revision should be the same but not for key1 and key2
+	newRevisions := make(map[string]string)
+	require.NoError(t, db.(*VersionedDB).addMissingRevisionsFromDB("ns1", []string{"key1", "key2", "key3"}, newRevisions))
+	require.Equal(t, 3, len(newRevisions))
+	require.NotEqual(t, revisions["key1"], newRevisions["key1"])
+	require.NotEqual(t, revisions["key2"], newRevisions["key2"])
+	require.Equal(t, revisions["key3"], newRevisions["key3"])
+}
+
+func TestMissingRevisionRetrievalFromCache(t *testing.T) {
+	cache := statedb.NewCache(32, []string{"lscc"})
+	env := newTestVDBEnvWithCache(t, cache)
+	defer env.Cleanup()
+	chainID := "testmissingrevisionfromcache"
+	db, err := env.DBProvider.GetDBHandle(chainID)
+	require.NoError(t, err)
+
+	// scenario 1: missing from cache.
+	revisions := make(map[string]string)
+	stillMissingKeys, err := db.(*VersionedDB).addMissingRevisionsFromCache("ns1", []string{"key1", "key2"}, revisions)
+	require.NoError(t, err)
+	require.Equal(t, []string{"key1", "key2"}, stillMissingKeys)
+	require.Empty(t, revisions)
+
+	// scenario 2: key1 is available in the cache
+	require.NoError(t, cache.PutState(chainID, "ns1", "key1", &statedb.CacheValue{AdditionalInfo: []byte("rev1")}))
+	revisions = make(map[string]string)
+	stillMissingKeys, err = db.(*VersionedDB).addMissingRevisionsFromCache("ns1", []string{"key1", "key2"}, revisions)
+	require.NoError(t, err)
+	require.Equal(t, []string{"key2"}, stillMissingKeys)
+	require.Equal(t, "rev1", revisions["key1"])
+
+	// scenario 3: both key1 and key2 are available in the cache
+	require.NoError(t, cache.PutState(chainID, "ns1", "key2", &statedb.CacheValue{AdditionalInfo: []byte("rev2")}))
+	revisions = make(map[string]string)
+	stillMissingKeys, err = db.(*VersionedDB).addMissingRevisionsFromCache("ns1", []string{"key1", "key2"}, revisions)
+	require.NoError(t, err)
+	require.Empty(t, stillMissingKeys)
+	require.Equal(t, "rev1", revisions["key1"])
+	require.Equal(t, "rev2", revisions["key2"])
+}