[Clipboard] Assert at least one clipboard data variant is provided

packages/flutter/lib/src/services/clipboard.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-
 import 'package:flutter/foundation.dart';
 
 import 'system_channels.dart';
@@ -14,9 +13,12 @@ import 'system_channels.dart';
 @immutable
 class ClipboardData {
   /// Creates data for the system clipboard.
-  const ClipboardData({ this.text });
+  const ClipboardData({ required String this.text });
 
   /// Plain text variant of this clipboard data.
+  // This is nullable as other clipboard data variants, like images, may be
+  // added in the future. Currently, plain text is the only supported variant
+  // and this is guaranteed to be non-null.
   final String? text;
 }
 
@@ -54,7 +56,7 @@ abstract final class Clipboard {
     if (result == null) {
       return null;
     }
-    return ClipboardData(text: result['text'] as String?);
+    return ClipboardData(text: result['text'] as String);
   }
 
   /// Returns a future that resolves to true iff the clipboard contains string

packages/flutter/test/services/clipboard_test.dart

@@ -0,0 +1,55 @@
+// Copyright 2014 The Flutter 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/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import '../widgets/clipboard_utils.dart';
+
+void main() {
+  final MockClipboard mockClipboard = MockClipboard();
+  TestWidgetsFlutterBinding.ensureInitialized()
+    .defaultBinaryMessenger.setMockMethodCallHandler(SystemChannels.platform, mockClipboard.handleMethodCall);
+
+  test('Clipboard.getData returns text', () async {
+    mockClipboard.clipboardData = <String, dynamic>{
+      'text': 'Hello world',
+    };
+
+    final ClipboardData? data = await Clipboard.getData(Clipboard.kTextPlain);
+
+    expect(data, isNotNull);
+    expect(data!.text, equals('Hello world'));
+  });
+
+  test('Clipboard.getData returns null', () async {
+    mockClipboard.clipboardData = null;
+
+    final ClipboardData? data = await Clipboard.getData(Clipboard.kTextPlain);
+
+    expect(data, isNull);
+  });
+
+  test('Clipboard.getData throws if text is missing', () async {
+    mockClipboard.clipboardData = <String, dynamic>{};
+
+    expect(() => Clipboard.getData(Clipboard.kTextPlain), throwsA(isA<TypeError>()));
+  });
+
+  test('Clipboard.getData throws if text is null', () async {
+    mockClipboard.clipboardData = <String, dynamic>{
+      'text': null,
+    };
+
+    expect(() => Clipboard.getData(Clipboard.kTextPlain), throwsA(isA<TypeError>()));
+  });
+
+  test('Clipboard.setData sets text', () async {
+    await Clipboard.setData(const ClipboardData(text: 'Hello world'));
+
+    expect(mockClipboard.clipboardData, <String, dynamic>{
+      'text': 'Hello world',
+    });
+  });
+}