Introduce DownloadJob for DownloadItem refactoring.

content/browser/download/download_job_unittest.cc

+// Copyright 2017 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 <memory>
+
+#include "base/memory/ptr_util.h"
+#include "content/browser/download/download_job.h"
+#include "content/browser/download/mock_download_job.h"
+#include "testing/gmock/include/gmock/gmock.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace content {
+
+class MockDownloadJobManager : public DownloadJob::Manager {
+ public:
+  MockDownloadJobManager() = default;
+  ~MockDownloadJobManager() = default;
+
+  MOCK_METHOD1(OnSavingStarted, void(DownloadJob* download_job));
+  MOCK_METHOD1(SetDangerType, void(DownloadDangerType));
+  MOCK_METHOD2(OnDownloadInterrupted,
+               void(DownloadJob* download_job, DownloadInterruptReason reason));
+  MOCK_METHOD1(OnDownloadComplete, void(DownloadJob* download_job));
+};
+
+// Test for DownloadJob base class functionalities.
+class DownloadJobTest : public testing::Test {
+ public:
+  DownloadJobTest() = default;
+  ~DownloadJobTest() override = default;
+
+  void SetUp() override {
+    download_job_manager_ = base::MakeUnique<MockDownloadJobManager>();
+    EXPECT_TRUE(download_job_manager_.get());
+    download_job_ = base::MakeUnique<MockDownloadJob>();
+  }
+
+  std::unique_ptr<MockDownloadJobManager> download_job_manager_;
+  std::unique_ptr<MockDownloadJob> download_job_;
+};
+
+TEST_F(DownloadJobTest, AttachAndDetach) {
+  // Ensure the manager should be valid only between attach and detach call.
+  EXPECT_FALSE(download_job_->manager());
+  download_job_->OnAttached(download_job_manager_.get());
+  EXPECT_TRUE(download_job_->manager());
+  download_job_->OnBeforeDetach();
+  EXPECT_FALSE(download_job_->manager());
+}
+
+}  // namespace content