emoji_reaction test: Check that RTL layout takes effect in test setup

We're about to refactor the way RTL gets applied.

While we're at it, also check the width of the ReactionChipsList
element.

Author: chrisbobbe

test/flutter_checks.dart

@@ -111,3 +111,13 @@ extension TypographyChecks on Subject<Typography> {
 extension InlineSpanChecks on Subject<InlineSpan> {
   Subject<TextStyle?> get style => has((x) => x.style, 'style');
 }
+
+extension SizeChecks on Subject<Size> {
+  Subject<double> get width => has((x) => x.width, 'width');
+  Subject<double> get height => has((x) => x.height, 'height');
+}
+
+extension ElementChecks on Subject<Element> {
+  Subject<Size?> get size => has((t) => t.size, 'size');
+  // TODO more
+}

test/widgets/emoji_reaction_test.dart

@@ -1,6 +1,7 @@
 import 'dart:io' as io;
 import 'dart:io';
 
+import 'package:checks/checks.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
@@ -13,6 +14,7 @@ import 'package:zulip/widgets/emoji_reaction.dart';
 import 'package:zulip/widgets/store.dart';
 
 import '../example_data.dart' as eg;
+import '../flutter_checks.dart';
 import '../model/binding.dart';
 import '../model/test_store.dart';
 import '../test_images.dart';
@@ -63,6 +65,10 @@ void main() {
 
       // global store, per-account store
       await tester.pumpAndSettle();
+
+      final reactionChipsList = tester.element(find.byType(ReactionChipsList));
+      check(Directionality.of(reactionChipsList)).equals(textDirection);
+      check(reactionChipsList).size.isNotNull().width.equals(width);
     }
 
     // Smoke tests under various conditions.