action_sheet test [nfc]: Parameterize a prepare by channel and topic

This `prepare` function would also be useful for some tests outside
the 'showTopicActionSheet' group. Give it these params to start
getting it ready to move to the outer scope. We'll add more params
in the next few commits.

Author: chrisbobbe

test/widgets/action_sheet_test.dart

@@ -108,21 +108,26 @@ void main() {
   }
 
   group('topic action sheet', () {
+    final someChannel = eg.stream();
+    const someTopic = 'my topic';
+
     group('showTopicActionSheet', () {
-      final channel = eg.stream();
-      const topic = 'my topic';
       final message = eg.streamMessage(
-        stream: channel, topic: topic, sender: eg.otherUser);
+        stream: someChannel, topic: someTopic, sender: eg.otherUser);
 
       Future<void> prepare({
+        ZulipStream? channel,
+        String topic = someTopic,
         UnreadMessagesSnapshot? unreadMsgs,
       }) async {
+        final effectiveChannel = channel ?? someChannel;
+
         addTearDown(testBinding.reset);
 
         await testBinding.globalStore.add(eg.selfAccount, eg.initialSnapshot(
           realmUsers: [eg.selfUser, eg.otherUser],
-          streams: [channel],
-          subscriptions: [eg.subscription(channel)],
+          streams: [effectiveChannel],
+          subscriptions: [eg.subscription(effectiveChannel)],
           unreadMsgs: unreadMsgs));
         store = await testBinding.globalStore.perAccount(eg.selfAccount.id);
         connection = store.connection as FakeApiConnection;
@@ -144,16 +149,16 @@ void main() {
       testWidgets('show from inbox', (tester) async {
         await prepare(unreadMsgs: eg.unreadMsgs(count: 1,
           channels: [eg.unreadChannelMsgs(
-            streamId: channel.streamId,
-            topic: topic,
+            streamId: someChannel.streamId,
+            topic: someTopic,
             unreadMessageIds: [message.id],
           )]));
         await tester.pumpWidget(TestZulipApp(accountId: eg.selfAccount.id,
           child: const HomePage()));
         await tester.pump();
         check(find.byType(InboxPageBody)).findsOne();
 
-        await tester.longPress(find.text(topic));
+        await tester.longPress(find.text(someTopic));
         // sheet appears onscreen; default duration of bottom-sheet enter animation
         await tester.pump(const Duration(milliseconds: 250));
         checkButtons();
@@ -165,11 +170,13 @@ void main() {
           foundOldest: true, messages: [message]).toJson());
         await tester.pumpWidget(TestZulipApp(accountId: eg.selfAccount.id,
           child: MessageListPage(
-            initNarrow: eg.topicNarrow(channel.streamId, topic))));
+            initNarrow: eg.topicNarrow(someChannel.streamId, someTopic))));
         // global store, per-account store, and message list get loaded
         await tester.pumpAndSettle();
 
-        final topicRow = find.descendant(of: find.byType(ZulipAppBar), matching: find.text(topic));
+        final topicRow = find.descendant(
+          of: find.byType(ZulipAppBar),
+          matching: find.text(someTopic));
         await tester.longPress(topicRow);
         // sheet appears onscreen; default duration of bottom-sheet enter animation
         await tester.pump(const Duration(milliseconds: 250));
@@ -186,7 +193,7 @@ void main() {
         await tester.pumpAndSettle();
 
         await tester.longPress(find.descendant(
-          of: find.byType(RecipientHeader), matching: find.text(topic)));
+          of: find.byType(RecipientHeader), matching: find.text(someTopic)));
         // sheet appears onscreen; default duration of bottom-sheet enter animation
         await tester.pump(const Duration(milliseconds: 250));
         checkButtons();