fix(cover): preserve provider high-resolution artwork

test/cover_art_utils_test.dart

@@ -0,0 +1,31 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:spotiflac_android/utils/cover_art_utils.dart';
+
+void main() {
+  group('highResCoverUrl', () {
+    test('upgrades a small Deezer cover to display quality', () {
+      expect(
+        highResCoverUrl(
+          'https://cdn-images.dzcdn.net/images/cover/hash/'
+          '250x250-000000-80-0-0.jpg',
+        ),
+        'https://cdn-images.dzcdn.net/images/cover/hash/'
+        '1000x1000-000000-80-0-0.jpg',
+      );
+    });
+
+    test('does not downgrade provider-supplied Deezer artwork', () {
+      const url =
+          'https://cdn-images.dzcdn.net/images/cover/hash/'
+          '1400x1400-000000-80-0-0.jpg';
+      expect(highResCoverUrl(url), url);
+    });
+
+    test('still upgrades a Spotify 300px cover to 640px', () {
+      expect(
+        highResCoverUrl('https://i.scdn.co/image/ab67616d00001e02abcdef'),
+        'https://i.scdn.co/image/ab67616d0000b273abcdef',
+      );
+    });
+  });
+}