Test print.dart (#7406)

packages/flutter/lib/src/foundation/print.dart

@@ -51,9 +51,9 @@ void debugPrintThrottled(String message, { int wrapWidth }) {
 }
 int _debugPrintedCharacters = 0;
 const int _kDebugPrintCapacity = 16 * 1024;
-Duration _kDebugPrintPauseTime = const Duration(seconds: 1);
-Queue<String> _debugPrintBuffer = new Queue<String>();
-Stopwatch _debugPrintStopwatch = new Stopwatch();
+const Duration _kDebugPrintPauseTime = const Duration(seconds: 1);
+final Queue<String> _debugPrintBuffer = new Queue<String>();
+final Stopwatch _debugPrintStopwatch = new Stopwatch();
 bool _debugPrintScheduled = false;
 void _debugPrintTask() {
   _debugPrintScheduled = false;

packages/flutter/test/foundation/print_test.dart

@@ -0,0 +1,75 @@
+// Copyright 2016 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 'dart:async';
+
+import 'package:flutter/foundation.dart';
+import 'package:quiver/testing/async.dart';
+import 'package:test/test.dart';
+
+List<String> captureOutput(VoidCallback fn) {
+  List<String> log = <String>[];
+
+  runZoned(fn, zoneSpecification: new ZoneSpecification(
+    print: (Zone self,
+            ZoneDelegate parent,
+            Zone zone,
+            String line) {
+              log.add(line);
+            },
+  ));
+
+  return log;
+}
+
+void main() {
+  test('debugPrint', () {
+    expect(
+      captureOutput(() { debugPrintSynchronously('Hello, world'); }),
+      equals(<String>['Hello, world'])
+    );
+
+    expect(
+      captureOutput(() { debugPrintSynchronously('Hello, world', wrapWidth: 10); }),
+      equals(<String>['Hello,\nworld'])
+    );
+
+    for (int i = 0; i < 14; ++i) {
+      expect(
+        captureOutput(() { debugPrintSynchronously('Hello,   world', wrapWidth: i); }),
+        equals(<String>['Hello,\nworld'])
+      );
+    }
+
+    expect(
+      captureOutput(() { debugPrintThrottled('Hello, world'); }),
+      equals(<String>['Hello, world'])
+    );
+
+    expect(
+      captureOutput(() { debugPrintThrottled('Hello, world', wrapWidth: 10); }),
+      equals(<String>['Hello,', 'world'])
+    );
+  });
+
+  test('debugPrint throttling', () {
+    new FakeAsync().run((FakeAsync async) {
+      List<String> log = captureOutput(() {
+        debugPrintThrottled('A' * (22 * 1024) + '\nB');
+      });
+      expect(log.length, 1);
+      async.elapse(const Duration(seconds: 2));
+      expect(log.length, 2);
+
+      log = captureOutput(() {
+        debugPrintThrottled('C' * (22 * 1024));
+        debugPrintThrottled('D');
+      });
+
+      expect(log.length, 1);
+      async.elapse(const Duration(seconds: 2));
+      expect(log.length, 2);
+    });
+  });
+}