Now returning duplicate database errors.

src/morethantext/cache.rs

@@ -43,7 +43,10 @@ impl Cache {
     pub fn commit(&mut self, data: Store) -> FromCache {
         let store = self.data.get_mut(ENTRY).unwrap();
         for name in data.list() {
-            store.add(name).unwrap();
+            match store.add(name) {
+                Ok(_) => (),
+                Err(err) => return FromCache::Error(err),
+            }
         }
         FromCache::Ok
     }

src/morethantext/mod.rs

@@ -146,6 +146,24 @@ mod mtt {
         let output = mtt1.session().await.unwrap();
         assert_eq!(output.list(), [db1, db2]);
     }
+
+    #[async_std::test]
+    async fn fail_on_duplicates() {
+        let dir = tempdir().unwrap();
+        let mtt1 = start_db(dir.path()).await.unwrap();
+        let mtt2 = mtt1.clone();
+        let name = "unique_only";
+        let mut store1 = mtt1.session().await.unwrap();
+        let mut store2 = mtt2.session().await.unwrap();
+        store1.add(name).unwrap();
+        store2.add(name).unwrap();
+        mtt1.commit(store1).await.unwrap();
+        let output = mtt2.commit(store2).await;
+        match output {
+            Ok(_) => assert!(false, "Should have returned an error"),
+            Err(_) => (),
+        }
+    }
 }
 
 pub async fn start_db<P>(dir: P) -> Result<MoreThanText, MTTError>