Switch newly added default Sources on once (#1)

The app now remembers which curated Sources it has seen. A Source that is on
by default is enabled the first time it appears, also on installs with saved
toggles; Sources seen before keep the user's choice. Installs from before this
change count the current catalog as seen.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/source_selection_test.dart

@@ -0,0 +1,89 @@
+import 'package:daily_tech_news/data/default_sources.dart';
+import 'package:daily_tech_news/models/news_source.dart';
+import 'package:daily_tech_news/services/feed_service.dart';
+import 'package:daily_tech_news/services/storage.dart';
+import 'package:daily_tech_news/state/app_state.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+/// Returns no articles, so starting the app doesn't hit the network.
+class _NoFeeds extends FeedService {
+  @override
+  Future<FeedResult> fetchAll(List<NewsSource> sources,
+          {required Duration maxAge, String corsProxy = ''}) async =>
+      const FeedResult([], {});
+}
+
+NewsSource _source(String id, {bool onByDefault = false}) => NewsSource(
+      id: id,
+      name: id,
+      feedUrl: 'https://example.com/$id.xml',
+      homepage: 'https://example.com',
+      language: SourceLanguage.en,
+      enabledByDefault: onByDefault,
+    );
+
+/// Starts the app the way a launch does, against whatever is in preferences.
+Future<AppState> _launch(List<NewsSource> curatedSources) async {
+  final state =
+      AppState(await Storage.open(), feedService: _NoFeeds(), curatedSources: curatedSources);
+  await state.init();
+  return state;
+}
+
+void main() {
+  final heise = _source('heise', onByDefault: true);
+  final golem = _source('golem', onByDefault: true);
+  final wired = _source('wired');
+
+  setUp(() => SharedPreferences.setMockInitialValues({}));
+
+  test('a fresh install starts with exactly the on-by-default Sources', () async {
+    final state = await _launch([heise, golem, wired]);
+
+    expect(state.enabledSourceIds, {'heise', 'golem'});
+  });
+
+  test('a newly added on-by-default Source shows up enabled after the update', () async {
+    final before = await _launch([heise, golem, wired]);
+    await before.setSourceEnabled(wired, true);
+
+    final verge = _source('verge', onByDefault: true);
+    final after = await _launch([heise, golem, wired, verge]);
+
+    expect(after.enabledSourceIds, {'heise', 'golem', 'wired', 'verge'});
+  });
+
+  test('a Source the user switched off stays off across updates', () async {
+    final before = await _launch([heise, golem, wired]);
+    await before.setSourceEnabled(golem, false);
+
+    final verge = _source('verge', onByDefault: true);
+    await _launch([heise, golem, wired, verge]);
+    final later = await _launch([heise, golem, wired, verge]);
+
+    expect(later.enabledSourceIds, {'heise', 'verge'});
+  });
+
+  test('a newly added Source that is off by default stays off', () async {
+    final before = await _launch([heise, golem, wired]);
+    await before.setSourceEnabled(wired, true);
+
+    final engadget = _source('engadget');
+    final after = await _launch([heise, golem, wired, engadget]);
+
+    expect(after.enabledSourceIds, {'heise', 'golem', 'wired'});
+  });
+
+  test('an install from before the app remembered seen Sources keeps its toggles', () async {
+    // Toggles saved by an earlier version: golem, t3n and others switched off.
+    SharedPreferences.setMockInitialValues({
+      'enabled_sources': ['heise', 'verge', 'wired'],
+    });
+
+    final newSource = _source('new-source', onByDefault: true);
+    final state = await _launch([...defaultSources, newSource]);
+
+    expect(state.enabledSourceIds, {'heise', 'verge', 'wired', 'new-source'});
+  });
+}