diff --git a/src/database/mod.rs b/src/database/mod.rs
index 711dea7ef..e3e2b3310 100644
--- a/src/database/mod.rs
+++ b/src/database/mod.rs
@@ -223,27 +223,27 @@ pub mod test {
 
     use super::*;
 
-    pub fn test_script_pubkey<D: Database>(mut tree: D) {
+    pub fn test_script_pubkey<D: Database>(mut db: D) {
         let script = Script::from(
             Vec::<u8>::from_hex("76a91402306a7c23f3e8010de41e9e591348bb83f11daa88ac").unwrap(),
         );
         let path = 42;
         let keychain = KeychainKind::External;
 
-        tree.set_script_pubkey(&script, keychain, path).unwrap();
+        db.set_script_pubkey(&script, keychain, path).unwrap();
 
         assert_eq!(
-            tree.get_script_pubkey_from_path(keychain, path).unwrap(),
+            db.get_script_pubkey_from_path(keychain, path).unwrap(),
             Some(script.clone())
         );
         assert_eq!(
-            tree.get_path_from_script_pubkey(&script).unwrap(),
+            db.get_path_from_script_pubkey(&script).unwrap(),
             Some((keychain, path))
         );
     }
 
-    pub fn test_batch_script_pubkey<D: BatchDatabase>(mut tree: D) {
-        let mut batch = tree.begin_batch();
+    pub fn test_batch_script_pubkey<D: BatchDatabase>(mut db: D) {
+        let mut batch = db.begin_batch();
 
         let script = Script::from(
             Vec::<u8>::from_hex("76a91402306a7c23f3e8010de41e9e591348bb83f11daa88ac").unwrap(),
@@ -254,50 +254,50 @@ pub mod test {
         batch.set_script_pubkey(&script, keychain, path).unwrap();
 
         assert_eq!(
-            tree.get_script_pubkey_from_path(keychain, path).unwrap(),
+            db.get_script_pubkey_from_path(keychain, path).unwrap(),
             None
         );
-        assert_eq!(tree.get_path_from_script_pubkey(&script).unwrap(), None);
+        assert_eq!(db.get_path_from_script_pubkey(&script).unwrap(), None);
 
-        tree.commit_batch(batch).unwrap();
+        db.commit_batch(batch).unwrap();
 
         assert_eq!(
-            tree.get_script_pubkey_from_path(keychain, path).unwrap(),
+            db.get_script_pubkey_from_path(keychain, path).unwrap(),
             Some(script.clone())
         );
         assert_eq!(
-            tree.get_path_from_script_pubkey(&script).unwrap(),
+            db.get_path_from_script_pubkey(&script).unwrap(),
             Some((keychain, path))
         );
     }
 
-    pub fn test_iter_script_pubkey<D: Database>(mut tree: D) {
+    pub fn test_iter_script_pubkey<D: Database>(mut db: D) {
         let script = Script::from(
             Vec::<u8>::from_hex("76a91402306a7c23f3e8010de41e9e591348bb83f11daa88ac").unwrap(),
         );
         let path = 42;
         let keychain = KeychainKind::External;
 
-        tree.set_script_pubkey(&script, keychain, path).unwrap();
+        db.set_script_pubkey(&script, keychain, path).unwrap();
 
-        assert_eq!(tree.iter_script_pubkeys(None).unwrap().len(), 1);
+        assert_eq!(db.iter_script_pubkeys(None).unwrap().len(), 1);
     }
 
-    pub fn test_del_script_pubkey<D: Database>(mut tree: D) {
+    pub fn test_del_script_pubkey<D: Database>(mut db: D) {
         let script = Script::from(
             Vec::<u8>::from_hex("76a91402306a7c23f3e8010de41e9e591348bb83f11daa88ac").unwrap(),
         );
         let path = 42;
         let keychain = KeychainKind::External;
 
-        tree.set_script_pubkey(&script, keychain, path).unwrap();
-        assert_eq!(tree.iter_script_pubkeys(None).unwrap().len(), 1);
+        db.set_script_pubkey(&script, keychain, path).unwrap();
+        assert_eq!(db.iter_script_pubkeys(None).unwrap().len(), 1);
 
-        tree.del_script_pubkey_from_path(keychain, path).unwrap();
-        assert_eq!(tree.iter_script_pubkeys(None).unwrap().len(), 0);
+        db.del_script_pubkey_from_path(keychain, path).unwrap();
+        assert_eq!(db.iter_script_pubkeys(None).unwrap().len(), 0);
     }
 
-    pub fn test_utxo<D: Database>(mut tree: D) {
+    pub fn test_utxo<D: Database>(mut db: D) {
         let outpoint = OutPoint::from_str(
             "5df6e0e2761359d30a8275058e299fcc0381534545f55cf43e41983f5d4c9456:0",
         )
@@ -316,21 +316,21 @@ pub mod test {
             is_spent: true,
         };
 
-        tree.set_utxo(&utxo).unwrap();
-        tree.set_utxo(&utxo).unwrap();
-        assert_eq!(tree.iter_utxos().unwrap().len(), 1);
-        assert_eq!(tree.get_utxo(&outpoint).unwrap(), Some(utxo));
+        db.set_utxo(&utxo).unwrap();
+        db.set_utxo(&utxo).unwrap();
+        assert_eq!(db.iter_utxos().unwrap().len(), 1);
+        assert_eq!(db.get_utxo(&outpoint).unwrap(), Some(utxo));
     }
 
-    pub fn test_raw_tx<D: Database>(mut tree: D) {
+    pub fn test_raw_tx<D: Database>(mut db: D) {
         let hex_tx = Vec::<u8>::from_hex("02000000000101f58c18a90d7a76b30c7e47d4e817adfdd79a6a589a615ef36e360f913adce2cd0000000000feffffff0210270000000000001600145c9a1816d38db5cbdd4b067b689dc19eb7d930e2cf70aa2b080000001600140f48b63160043047f4f60f7f8f551f80458f693f024730440220413f42b7bc979945489a38f5221e5527d4b8e3aa63eae2099e01945896ad6c10022024ceec492d685c31d8adb64e935a06933877c5ae0e21f32efe029850914c5bad012102361caae96f0e9f3a453d354bb37a5c3244422fb22819bf0166c0647a38de39f21fca2300").unwrap();
         let mut tx: Transaction = deserialize(&hex_tx).unwrap();
 
-        tree.set_raw_tx(&tx).unwrap();
+        db.set_raw_tx(&tx).unwrap();
 
         let txid = tx.txid();
 
-        assert_eq!(tree.get_raw_tx(&txid).unwrap(), Some(tx.clone()));
+        assert_eq!(db.get_raw_tx(&txid).unwrap(), Some(tx.clone()));
 
         // mutate transaction's witnesses
         for tx_in in tx.input.iter_mut() {
@@ -342,14 +342,14 @@ pub mod test {
         // verify that mutation was successful
         assert_ne!(hex_tx, updated_hex_tx);
 
-        tree.set_raw_tx(&tx).unwrap();
+        db.set_raw_tx(&tx).unwrap();
 
         let txid = tx.txid();
 
-        assert_eq!(tree.get_raw_tx(&txid).unwrap(), Some(tx));
+        assert_eq!(db.get_raw_tx(&txid).unwrap(), Some(tx));
     }
 
-    pub fn test_tx<D: Database>(mut tree: D) {
+    pub fn test_tx<D: Database>(mut db: D) {
         let hex_tx = Vec::<u8>::from_hex("0100000001a15d57094aa7a21a28cb20b59aab8fc7d1149a3bdbcddba9c622e4f5f6a99ece010000006c493046022100f93bb0e7d8db7bd46e40132d1f8242026e045f03a0efe71bbb8e3f475e970d790221009337cd7f1f929f00cc6ff01f03729b069a7c21b59b1736ddfee5db5946c5da8c0121033b9b137ee87d5a812d6f506efdd37f0affa7ffc310711c06c7f3e097c9447c52ffffffff0100e1f505000000001976a9140389035a9225b3839e2bbf32d826a1e222031fd888ac00000000").unwrap();
         let tx: Transaction = deserialize(&hex_tx).unwrap();
         let txid = tx.txid();
@@ -365,28 +365,28 @@ pub mod test {
             }),
         };
 
-        tree.set_tx(&tx_details).unwrap();
+        db.set_tx(&tx_details).unwrap();
 
         // get with raw tx too
         assert_eq!(
-            tree.get_tx(&tx_details.txid, true).unwrap(),
+            db.get_tx(&tx_details.txid, true).unwrap(),
             Some(tx_details.clone())
         );
         // get only raw_tx
         assert_eq!(
-            tree.get_raw_tx(&tx_details.txid).unwrap(),
+            db.get_raw_tx(&tx_details.txid).unwrap(),
             tx_details.transaction
         );
 
         // now get without raw_tx
         tx_details.transaction = None;
         assert_eq!(
-            tree.get_tx(&tx_details.txid, false).unwrap(),
+            db.get_tx(&tx_details.txid, false).unwrap(),
             Some(tx_details)
         );
     }
 
-    pub fn test_list_transaction<D: Database>(mut tree: D) {
+    pub fn test_list_transaction<D: Database>(mut db: D) {
         let hex_tx = Vec::<u8>::from_hex("0100000001a15d57094aa7a21a28cb20b59aab8fc7d1149a3bdbcddba9c622e4f5f6a99ece010000006c493046022100f93bb0e7d8db7bd46e40132d1f8242026e045f03a0efe71bbb8e3f475e970d790221009337cd7f1f929f00cc6ff01f03729b069a7c21b59b1736ddfee5db5946c5da8c0121033b9b137ee87d5a812d6f506efdd37f0affa7ffc310711c06c7f3e097c9447c52ffffffff0100e1f505000000001976a9140389035a9225b3839e2bbf32d826a1e222031fd888ac00000000").unwrap();
         let tx: Transaction = deserialize(&hex_tx).unwrap();
         let txid = tx.txid();
@@ -402,46 +402,43 @@ pub mod test {
             }),
         };
 
-        tree.set_tx(&tx_details).unwrap();
+        db.set_tx(&tx_details).unwrap();
 
         // get raw tx
-        assert_eq!(tree.iter_txs(true).unwrap(), vec![tx_details.clone()]);
+        assert_eq!(db.iter_txs(true).unwrap(), vec![tx_details.clone()]);
 
         // now get without raw tx
         tx_details.transaction = None;
 
         // get not raw tx
-        assert_eq!(tree.iter_txs(false).unwrap(), vec![tx_details.clone()]);
+        assert_eq!(db.iter_txs(false).unwrap(), vec![tx_details.clone()]);
     }
 
-    pub fn test_last_index<D: Database>(mut tree: D) {
-        tree.set_last_index(KeychainKind::External, 1337).unwrap();
+    pub fn test_last_index<D: Database>(mut db: D) {
+        db.set_last_index(KeychainKind::External, 1337).unwrap();
 
         assert_eq!(
-            tree.get_last_index(KeychainKind::External).unwrap(),
+            db.get_last_index(KeychainKind::External).unwrap(),
             Some(1337)
         );
-        assert_eq!(tree.get_last_index(KeychainKind::Internal).unwrap(), None);
+        assert_eq!(db.get_last_index(KeychainKind::Internal).unwrap(), None);
 
-        let res = tree.increment_last_index(KeychainKind::External).unwrap();
+        let res = db.increment_last_index(KeychainKind::External).unwrap();
         assert_eq!(res, 1338);
-        let res = tree.increment_last_index(KeychainKind::Internal).unwrap();
+        let res = db.increment_last_index(KeychainKind::Internal).unwrap();
         assert_eq!(res, 0);
 
         assert_eq!(
-            tree.get_last_index(KeychainKind::External).unwrap(),
+            db.get_last_index(KeychainKind::External).unwrap(),
             Some(1338)
         );
-        assert_eq!(
-            tree.get_last_index(KeychainKind::Internal).unwrap(),
-            Some(0)
-        );
+        assert_eq!(db.get_last_index(KeychainKind::Internal).unwrap(), Some(0));
     }
 
-    pub fn test_sync_time<D: Database>(mut tree: D) {
-        assert!(tree.get_sync_time().unwrap().is_none());
+    pub fn test_sync_time<D: Database>(mut db: D) {
+        assert!(db.get_sync_time().unwrap().is_none());
 
-        tree.set_sync_time(SyncTime {
+        db.set_sync_time(SyncTime {
             block_time: BlockTime {
                 height: 100,
                 timestamp: 1000,
@@ -449,13 +446,13 @@ pub mod test {
         })
         .unwrap();
 
-        let extracted = tree.get_sync_time().unwrap();
+        let extracted = db.get_sync_time().unwrap();
         assert!(extracted.is_some());
         assert_eq!(extracted.as_ref().unwrap().block_time.height, 100);
         assert_eq!(extracted.as_ref().unwrap().block_time.timestamp, 1000);
 
-        tree.del_sync_time().unwrap();
-        assert!(tree.get_sync_time().unwrap().is_none());
+        db.del_sync_time().unwrap();
+        assert!(db.get_sync_time().unwrap().is_none());
     }
 
     pub fn test_iter_raw_txs<D: Database>(mut db: D) {