Use the glossary's words in test names and comments (review item 2)

"Feed" no longer stands for a Source and "newsletter" no longer for a
Learning source; paid_newsletter_posts_test.dart becomes
paid_substack_posts_test.dart.

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

test/learn_tab_test.dart

@@ -73,7 +73,7 @@ void main() {
     expect(find.byType(SettingsScreen), findsOneWidget);
   });
 
-  testWidgets('leaving the Sources tab after a change refreshes the feeds', (tester) async {
+  testWidgets('leaving the Sources tab after a change refreshes all Sources', (tester) async {
     final feedService = FakeFeeds(feeds);
     final state = await launch(tester, feedService);
     await tester.pumpWidget(MaterialApp(home: HomeShell(state: state)));

test/paid_substack_posts_test.dart

@@ -47,7 +47,7 @@ void main() {
         substackNews.feedUrl: 'test/fixtures/ahead_of_ai_feed.xml',
       });
 
-  test('paid newsletter posts are hidden in the Learn tab and Today and counted as hidden',
+  test('paid Substack posts are hidden in the Learn tab and Today and counted as hidden',
       () async {
     final state = await launchApp([interconnects, substackNews], feedService: savedFeeds());
 
@@ -61,7 +61,7 @@ void main() {
     expect(state.hiddenCountOf(SourceKind.news), 1);
   });
 
-  test('with "hide paid articles" off, paid newsletter posts show as before', () async {
+  test('with "hide paid articles" off, paid Substack posts show as before', () async {
     final state = await launchApp([interconnects, substackNews], feedService: savedFeeds());
 
     await state.updateSettings(state.settings.copyWith(hidePaid: false));

test/sources_tab_test.dart

@@ -80,7 +80,7 @@ void main() {
     expect(find.text(german), findsNothing);
   });
 
-  Future<void> addFeed(WidgetTester tester, String name, {String? kind}) async {
+  Future<void> addSource(WidgetTester tester, String name, {String? kind}) async {
     await tester.tap(find.text('Add feed'));
     await tester.pumpAndSettle();
     final dialog = find.byType(AlertDialog);
@@ -97,29 +97,29 @@ void main() {
     await tester.pumpAndSettle();
   }
 
-  testWidgets('a feed added without picking a kind is a News source', (tester) async {
+  testWidgets('a Source added without picking a kind is a News source', (tester) async {
     final state = await launch(tester, [verge, bytebytego]);
     await showSources(tester, state);
 
-    await addFeed(tester, 'myfeed');
+    await addSource(tester, 'myfeed');
 
     expectInOrder(tester, [find.text('News'), find.text('myfeed'), find.text('Learning')]);
   });
 
-  testWidgets('a feed added as Learning shows up in the Learning section', (tester) async {
+  testWidgets('a Source added as Learning shows up in the Learning section', (tester) async {
     final state = await launch(tester, [verge, bytebytego]);
     await showSources(tester, state);
 
-    await addFeed(tester, 'myblog', kind: 'Learning');
+    await addSource(tester, 'myblog', kind: 'Learning');
 
     expectInOrder(tester, [find.text('Learning'), find.text('myblog')]);
   });
 
-  testWidgets('a feed added as Fun gets a Fun section', (tester) async {
+  testWidgets('a Source added as Fun gets a Fun section', (tester) async {
     final state = await launch(tester, [verge]);
     await showSources(tester, state);
 
-    await addFeed(tester, 'mycomic', kind: 'Fun');
+    await addSource(tester, 'mycomic', kind: 'Fun');
 
     expectInOrder(tester, [find.text('News'), find.text('Fun'), find.text('mycomic')]);
   });
@@ -140,7 +140,7 @@ void main() {
 
     await tester.tap(tab('Sources'));
     await tester.pump();
-    await addFeed(tester, 'myblog', kind: 'Learning');
+    await addSource(tester, 'myblog', kind: 'Learning');
     await tester.tap(tab('Learn'));
     await tester.pumpAndSettle();
 
@@ -170,7 +170,7 @@ void main() {
 
     await tester.tap(tab('Sources'));
     await tester.pump();
-    await addFeed(tester, 'mycomic', kind: 'Fun');
+    await addSource(tester, 'mycomic', kind: 'Fun');
     await tester.tap(tab('Learn'));
     await tester.pumpAndSettle();
 

test/support/fake_app.dart

@@ -14,7 +14,7 @@ class FakeFeeds extends FeedService {
   /// Feed URL -> (title, age) of each article in the feed.
   final Map<String, List<(String, Duration)>> byFeedUrl;
 
-  /// How often the app refreshed its feeds.
+  /// How often the app refreshed all Sources.
   int refreshes = 0;
 
   @override