Adds some tests related to transactions

lib/src/store/rocksdb.rs

@@ -1231,10 +1231,16 @@ fn store() -> Result<(), io::Error> {
 
     {
         let store = RocksDbStore::open(&repo_path)?;
-        for t in &all_quads {
+        for t in &default_quads {
             store.insert(t)?;
         }
 
+        store.transaction(|t| {
+            t.remove(&default_quad)?;
+            t.insert(&named_quad)?;
+            t.insert(&default_quad)
+        })?;
+
         assert_eq!(store.len(), 4);
         assert_eq!(
             store

lib/src/store/sled.rs

@@ -1280,10 +1280,18 @@ fn store() -> Result<(), io::Error> {
     ];
 
     let store = SledStore::new()?;
-    for t in &all_quads {
+    for t in &default_quads {
         store.insert(t)?;
     }
 
+    let result: Result<_, SledTransactionError<io::Error>> = store.transaction(|t| {
+        t.remove(&default_quad)?;
+        t.insert(&named_quad)?;
+        t.insert(&default_quad)?;
+        Ok(())
+    });
+    result?;
+
     assert_eq!(store.len(), 4);
     assert_eq!(
         store