Allow ScopedTaskScheduler to be created before a class that overrides MessageLoop::current()'s task…

base/test/scoped_task_scheduler_unittest.cc

 // 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.
 
 #include "base/test/scoped_task_scheduler.h"
 
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/run_loop.h"
 #include "base/sequence_checker.h"
 #include "base/task_scheduler/post_task.h"
 #include "base/task_scheduler/task_scheduler.h"
 #include "base/task_scheduler/test_utils.h"
+#include "base/test/scoped_mock_time_message_loop_task_runner.h"
 #include "base/threading/sequenced_task_runner_handle.h"
 #include "base/threading/thread_checker.h"
 #include "base/threading/thread_task_runner_handle.h"
+#include "base/time/time.h"
 #include "build/build_config.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
 namespace test {
 
 TEST(ScopedTaskSchedulerTest, PostTask) {
   ScopedTaskScheduler scoped_task_scheduler;
 
   bool first_task_ran = false;
@@ skipping 232 matching lines @@
                                       TaskShutdownBehavior::BLOCK_SHUTDOWN),
                        Bind(
                            [](bool* block_shutdown_task_ran) {
                              *block_shutdown_task_ran = true;
                            },
                            Unretained(&block_shutdown_task_ran)));
   }
   EXPECT_TRUE(block_shutdown_task_ran);
 }
 
+TEST(ScopedTaskSchedulerTest, ReassignCurrentTaskRunner) {
+  bool first_task_ran = false;
+  bool second_task_ran = false;
+
+  auto TestTaskRan = [](bool* task_ran) { *task_ran = true; };
+
+  ScopedTaskScheduler scoped_task_scheduler;
+  {
+    ScopedMockTimeMessageLoopTaskRunner mock_time_task_runner;
+    PostDelayedTask(FROM_HERE, Bind(TestTaskRan, Unretained(&first_task_ran)),
+                    TimeDelta::FromSeconds(1));
+
+    // The delayed task should be queued on |mock_time_task_runner|, not the
+    // default task runner.
+    EXPECT_TRUE(mock_time_task_runner.task_runner()->HasPendingTask());
+  }
+
+  PostDelayedTask(FROM_HERE, Bind(TestTaskRan, Unretained(&second_task_ran)),
+                  TimeDelta());
+
+  RunLoop().RunUntilIdle();
+
+  // We never pumped |mock_time_task_runner| so the first task should not have
+  // run.
+  EXPECT_FALSE(first_task_ran);
+  EXPECT_TRUE(second_task_ran);
+}
+
 }  // namespace test
 }  // namespace base