Add Isolates test

@@ -20,6 +20,7 @@ import '../example/main.dart' as example;
 import 'annotations_test.dart' as annotations;
 import 'colors_test.dart' as colors;
 import 'complex_test.dart' as complex;
+import 'isolate_test.dart' as isolate;
 import 'jpeg_test.dart' as jpeg;
 import 'metrics_test.dart' as metrics;
 import 'minimal_test.dart' as minimal;
@@ -40,6 +41,7 @@ void main() {
   colors.main();
   complex.main();
   example.main();
+  isolate.main();
   jpeg.main();
   metrics.main();
   minimal.main();

+/*
+ * Copyright (C) 2017, David PHAM-VAN <dev.nfet.net@gmail.com>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import 'dart:async';
+import 'dart:io';
+import 'dart:isolate';
+import 'dart:typed_data';
+
+import 'package:pdf/pdf.dart';
+import 'package:pdf/widgets.dart';
+import 'package:test/test.dart';
+
+class Message {
+  Message(this.image, this.sendPort);
+
+  final Uint8List image;
+  final SendPort sendPort;
+}
+
+Future<Uint8List> download(String url) async {
+  final HttpClient client = HttpClient();
+  final HttpClientRequest request = await client.getUrl(Uri.parse(url));
+  final HttpClientResponse response = await request.close();
+  final BytesBuilder builder = await response.fold(
+      BytesBuilder(), (BytesBuilder b, List<int> d) => b..add(d));
+  final List<int> data = builder.takeBytes();
+  return Uint8List.fromList(data);
+}
+
+void compute(Message message) {
+  final Document pdf = Document();
+
+  final PdfImage image = PdfImage.jpeg(
+    pdf.document,
+    image: message.image,
+  );
+
+  pdf.addPage(Page(build: (Context context) => Center(child: Image(image))));
+
+  message.sendPort.send(pdf.save());
+}
+
+void main() {
+  test('Pdf Isolate', () async {
+    final Completer<void> completer = Completer<void>();
+    final ReceivePort receivePort = ReceivePort();
+
+    receivePort.listen((dynamic data) async {
+      if (data is List<int>) {
+        print('Received a ${data.length} bytes PDF');
+        final File file = File('isolate.pdf');
+        await file.writeAsBytes(data);
+        print('File saved');
+      }
+      completer.complete();
+    });
+
+    print('Download image');
+    final Uint8List imageBytes =
+        await download('https://www.nfet.net/nfet.jpg');
+
+    print('Generate PDF');
+    await Isolate.spawn<Message>(
+      compute,
+      Message(imageBytes, receivePort.sendPort),
+    );
+
+    print('Wait PDF to be generated');
+    await completer.future;
+    print('Done');
+  });
+}