autocomplete test: Add test case for delivery email visibility

Checks delivery email is visible only when its not null,
and the server generated fake email isn't shown.
Also fixes minor bug in example_data.dart which
causes delivery email to always be shown in tests.

Author: fombalang

test/example_data.dart

@@ -125,7 +125,7 @@ User user({
   _checkPositive(userId, 'user ID');
   return User(
     userId: userId ?? _nextUserId(),
-    deliveryEmail: effectiveDeliveryEmail,
+    deliveryEmail: deliveryEmail,
     email: email ?? effectiveDeliveryEmail,
     fullName: fullName ?? 'A user', // TODO generate example names
     dateJoined: dateJoined ?? '2024-02-24T11:18+00:00',

test/widgets/autocomplete_test.dart

@@ -131,9 +131,10 @@ void main() {
     Finder findAvatarImage(int userId) =>
       find.byWidgetPredicate((widget) => widget is AvatarImage && widget.userId == userId);
 
-    void checkUserShown(User user, {required bool expected}) {
+    void checkUserShown(User user, {required bool expected, bool? deliveryEmailExpected}) {
+      deliveryEmailExpected ??= expected;
       check(find.text(user.fullName).evaluate().length).equals(expected ? 1 : 0);
-      check(find.text(user.deliveryEmail!).evaluate().length).equals(expected ? 1 : 0);
+      check(find.text(user.deliveryEmail?? "").evaluate().length).equals(deliveryEmailExpected ? 1 : 0);
       final avatarFinder = findAvatarImage(user.userId);
       check(avatarFinder.evaluate().length).equals(expected ? 1 : 0);
     }
@@ -182,6 +183,27 @@ void main() {
 
       debugNetworkImageHttpClientProvider = null;
     });
+
+    testWidgets('test delivery email visibility', (tester) async {
+      final user2 = eg.user(userId: 2, fullName: 'User Two', avatarUrl: 'user2.png',);
+      final user3 = eg.user(userId: 3, fullName: 'User Three', avatarUrl: 'user3.png', deliveryEmail: '[email protected]');
+      final composeInputFinder = await setupToComposeInput(tester, users: [user2, user3]);
+
+      TypingNotifier.debugEnable = false;
+      addTearDown(TypingNotifier.debugReset);
+
+      // Options are filtered correctly for query
+      // TODO(#226): Remove this extra edit when this bug is fixed.
+      await tester.enterText(composeInputFinder, 'hello @user ');
+      await tester.enterText(composeInputFinder, 'hello @user t');
+      await tester.pumpAndSettle(); // async computation; options appear
+
+      // "User Two"'s delivery email is not visible and "User Three"'s delivery email is visible
+      checkUserShown(user2, expected: true, deliveryEmailExpected: false);
+      checkUserShown(user3, expected: true, deliveryEmailExpected: true);
+
+      debugNetworkImageHttpClientProvider = null;
+    });
   });
 
   group('emoji', () {