Add:创建 flutter go web 版

packages/flutter_web/test/widgets/directionality_test.dart

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+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter_web_test/flutter_web_test.dart';
+import 'package:flutter_web/widgets.dart';
+
+void main() {
+  testWidgets('Directionality', (WidgetTester tester) async {
+    final List<TextDirection> log = <TextDirection>[];
+    final Widget inner = Builder(builder: (BuildContext context) {
+      log.add(Directionality.of(context));
+      return const Placeholder();
+    });
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: inner,
+      ),
+    );
+    expect(log, <TextDirection>[TextDirection.ltr]);
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: inner,
+      ),
+    );
+    expect(log, <TextDirection>[TextDirection.ltr]);
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.rtl,
+        child: inner,
+      ),
+    );
+    expect(log, <TextDirection>[TextDirection.ltr, TextDirection.rtl]);
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.rtl,
+        child: inner,
+      ),
+    );
+    expect(log, <TextDirection>[TextDirection.ltr, TextDirection.rtl]);
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: inner,
+      ),
+    );
+    expect(log, <TextDirection>[
+      TextDirection.ltr,
+      TextDirection.rtl,
+      TextDirection.ltr
+    ]);
+  });
+
+  testWidgets('Directionality default', (WidgetTester tester) async {
+    bool good = false;
+    await tester.pumpWidget(Builder(
+      builder: (BuildContext context) {
+        expect(Directionality.of(context), isNull);
+        good = true;
+        return const Placeholder();
+      },
+    ));
+    expect(good, isTrue);
+  });
+
+  testWidgets('Directionality can\'t be null', (WidgetTester tester) async {
+    expect(() {
+      Directionality(textDirection: nonconst(null), child: const Placeholder());
+    }, throwsAssertionError);
+  });
+}