Reproduce #108 in a unit test

src/lib.rs

@@ -1975,6 +1975,34 @@ mod tests {
         assert_eq!(expected, merged);
     }
 
+    #[test]
+    fn merge_collection_incompatible_sorting() {
+        // It may be that the same artist in one collection has a "sort" field defined while the
+        // same artist in the other collection does not. This means that the two collections are not
+        // sorted consistently. If the merge assumes they are sorted consistently this will lead to
+        // the same artist appearing twice in the final list. This should not be the case.
+
+        // We will mimic this situation by taking the last artist from COLLECTION and giving it a
+        // sorting name that would place it in the beginning.
+        let left = COLLECTION.to_owned();
+        let mut right: Vec<Artist> = vec![left.last().unwrap().clone()];
+
+        assert!(right.first().unwrap() > left.first().unwrap());
+        let artist_sort = Some(ArtistId::new("album_artist 0"));
+        right[0].sort = artist_sort.clone();
+        assert!(right.first().unwrap() < left.first().unwrap());
+
+        // The result of the merge should be the same list of artists, but with the last artist now
+        // in first place.
+        let mut expected = left.to_owned();
+        expected.last_mut().map(|a| a.sort = artist_sort.clone());
+        expected.rotate_right(1);
+
+        let merged = MusicHoard::<NoLibrary, NoDatabase>::merge(left.clone(), right);
+        assert_eq!(expected.len(), merged.len());
+        assert_eq!(expected, merged);
+    }
+
     #[test]
     fn rescan_library_ordered() {
         let mut library = MockILibrary::new();