Add UT for date merge

src/core/collection/album.rs

@@ -419,4 +419,39 @@ mod tests {
         let merged = left.clone().merge(right);
         assert_eq!(expected, merged);
     }
+
+    #[test]
+    fn merge_album_dates() {
+        let meta = AlbumMeta::new(AlbumId::new("An album"));
+
+        // No merge if years are different.
+        let left = meta.clone().with_date((2000, 1, 6));
+        let right = meta.clone().with_date((1000, 2, 7));
+        let expected = meta.clone().with_date(left.date);
+        assert_eq!(expected, left.merge(right));
+
+        // No merge if years are the same but months/days are different.
+        let left = meta.clone().with_date((2000, 1, 6));
+        let right = meta.clone().with_date((2000, 2, 7));
+        let expected = meta.clone().with_date(left.date);
+        assert_eq!(expected, left.merge(right));
+
+        // No merge if right has no date.
+        let left = meta.clone().with_date((2000, 1, 6));
+        let right = meta.clone();
+        let expected = meta.clone().with_date(left.date);
+        assert_eq!(expected, left.merge(right));
+
+        // Merge if left has no date.
+        let left = meta.clone();
+        let right = meta.clone().with_date((2000, 2, 7));
+        let expected = meta.clone().with_date(right.date);
+        assert_eq!(expected, left.merge(right));
+
+        // Merge if left has no year but has months/days.
+        let left = meta.clone().with_date(AlbumDate::new(None, Some(1), Some(6)));
+        let right = meta.clone().with_date((2000, 2, 7));
+        let expected = meta.clone().with_date(right.date);
+        assert_eq!(expected, left.merge(right));
+    }
 }