diff --git a/buffet/xmpp/xmpp_client_unittest.cc b/buffet/xmpp/xmpp_client_unittest.cc
new file mode 100644
index 0000000..9736349
--- /dev/null
+++ b/buffet/xmpp/xmpp_client_unittest.cc
@@ -0,0 +1,208 @@
+// Copyright 2015 The Chromium OS 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 "buffet/device_registration_info.h"
+
+#include <base/values.h>
+#include <chromeos/key_value_store.h>
+#include <chromeos/http/curl_api.h>
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+
+#include "buffet/xmpp/xmpp_client.h"
+#include "buffet/xmpp/xmpp_connection.h"
+
+using ::testing::DoAll;
+using ::testing::Return;
+using ::testing::SetArgPointee;
+using ::testing::_;
+
+namespace buffet {
+
+namespace {
+
+constexpr char kAccountName[] = "Account@Name";
+constexpr char kAccessToken[] = "AccessToken";
+
+constexpr char kStartStreamResponse[] =
+    "<stream:stream from=\"clouddevices.gserviceaccount.com\" "
+    "id=\"0CCF520913ABA04B\" version=\"1.0\" "
+    "xmlns:stream=\"http://etherx.jabber.org/streams\" "
+    "xmlns=\"jabber:client\">"
+    "<stream:features><starttls xmlns=\"urn:ietf:params:xml:ns:xmpp-tls\">"
+    "<required/></starttls><mechanisms "
+    "xmlns=\"urn:ietf:params:xml:ns:xmpp-sasl\"><mechanism>X-OAUTH2</mechanism>"
+    "<mechanism>X-GOOGLE-TOKEN</mechanism></mechanisms></stream:features>";
+constexpr char kAuthenticationResponse[] =
+    "<success xmlns=\"urn:ietf:params:xml:ns:xmpp-sasl\"/>";
+constexpr char kRestartStreamResponse[] =
+    "<stream:stream from=\"clouddevices.gserviceaccount.com\" "
+    "id=\"BE7D34E0B7589E2A\" version=\"1.0\" "
+    "xmlns:stream=\"http://etherx.jabber.org/streams\" "
+    "xmlns=\"jabber:client\">"
+    "<stream:features><bind xmlns=\"urn:ietf:params:xml:ns:xmpp-bind\"/>"
+    "<session xmlns=\"urn:ietf:params:xml:ns:xmpp-session\"/>"
+    "</stream:features>";
+constexpr char kBindResponse[] =
+    "<iq id=\"0\" type=\"result\">"
+    "<bind xmlns=\"urn:ietf:params:xml:ns:xmpp-bind\">"
+    "<jid>110cc78f78d7032cc7bf2c6e14c1fa7d@clouddevices.gserviceaccount.com"
+    "/19853128</jid></bind></iq>";
+constexpr char kSessionResponse[] =
+    "<iq type=\"result\" id=\"1\"/>";
+constexpr char kSubscribedResponse[] =
+    "<iq to=\""
+    "110cc78f78d7032cc7bf2c6e14c1fa7d@clouddevices.gserviceaccount.com/"
+    "19853128\" from=\""
+    "110cc78f78d7032cc7bf2c6e14c1fa7d@clouddevices.gserviceaccount.com\" "
+    "id=\"pushsubscribe1\" type=\"result\"/>";
+
+constexpr char kStartStreamMessage[] =
+    "<stream:stream to='clouddevices.gserviceaccount.com' "
+    "xmlns:stream='http://etherx.jabber.org/streams' xml:lang='*' "
+    "version='1.0' xmlns='jabber:client'>";
+constexpr char kAuthenticationMessage[] =
+    "<auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl' mechanism='X-OAUTH2' "
+    "auth:service='oauth2' auth:allow-non-google-login='true' "
+    "auth:client-uses-full-bind-result='true' "
+    "xmlns:auth='http://www.google.com/talk/protocol/auth'>"
+    "AEFjY291bnRATmFtZQBBY2Nlc3NUb2tlbg==</auth>";
+constexpr char kBindMessage[] =
+    "<iq type='set' id='0'><bind "
+    "xmlns='urn:ietf:params:xml:ns:xmpp-bind'/></iq>";
+constexpr char kSessionMessage[] =
+    "<iq type='set' id='1'><session "
+    "xmlns='urn:ietf:params:xml:ns:xmpp-session'/></iq>";
+constexpr char kSubscribeMessage[] =
+    "<iq type='set' to='Account@Name' id='pushsubscribe1'>"
+    "<subscribe xmlns='google:push'><item channel='cloud_devices' from=''/>"
+    "</subscribe></iq>";
+
+class MockXmppConnection : public XmppConnection {
+ public:
+  MockXmppConnection() = default;
+
+  MOCK_CONST_METHOD1(Read, bool(std::string* msg));
+  MOCK_CONST_METHOD1(Write, bool(const std::string& msg));
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MockXmppConnection);
+};
+
+}  // namespace
+
+class TestHelper {
+ public:
+  static void SetState(XmppClient* client, XmppClient::XmppState state) {
+    client->state_ = state;
+  }
+
+  static XmppClient::XmppState GetState(const XmppClient& client) {
+    return client.state_;
+  }
+
+  static XmppConnection* GetConnection(const XmppClient& client) {
+    return client.connection_.get();
+  }
+};
+
+class XmppClientTest : public ::testing::Test {
+ protected:
+  void SetUp() override {
+    std::unique_ptr<XmppConnection> connection(new MockXmppConnection());
+    xmpp_client_.reset(new XmppClient(kAccountName, kAccessToken,
+                                      std::move(connection)));
+    connection_ = static_cast<MockXmppConnection*>(
+        TestHelper::GetConnection(*xmpp_client_));
+  }
+
+  std::unique_ptr<XmppClient> xmpp_client_;
+  MockXmppConnection* connection_;  // xmpp_client_ owns this.
+};
+
+TEST_F(XmppClientTest, StartStream) {
+  EXPECT_EQ(TestHelper::GetState(*xmpp_client_),
+            XmppClient::XmppState::kNotStarted);
+  EXPECT_CALL(*connection_, Write(kStartStreamMessage))
+      .WillOnce(Return(true));
+  xmpp_client_->StartStream();
+  EXPECT_EQ(TestHelper::GetState(*xmpp_client_),
+            XmppClient::XmppState::kStarted);
+}
+
+TEST_F(XmppClientTest, HandleStartedResponse) {
+  TestHelper::SetState(xmpp_client_.get(),
+                       XmppClient::XmppState::kStarted);
+  EXPECT_CALL(*connection_, Read(_))
+      .WillOnce(DoAll(SetArgPointee<0>(kStartStreamResponse), Return(true)));
+  EXPECT_CALL(*connection_, Write(kAuthenticationMessage))
+      .WillOnce(Return(true));
+  xmpp_client_->Read();
+  EXPECT_EQ(TestHelper::GetState(*xmpp_client_),
+            XmppClient::XmppState::kAuthenticationStarted);
+}
+
+TEST_F(XmppClientTest, HandleAuthenticationResponse) {
+  TestHelper::SetState(
+      xmpp_client_.get(),
+      XmppClient::XmppState::kAuthenticationStarted);
+  EXPECT_CALL(*connection_, Read(_))
+      .WillOnce(DoAll(SetArgPointee<0>(kAuthenticationResponse), Return(true)));
+  EXPECT_CALL(*connection_, Write(kStartStreamMessage))
+      .WillOnce(Return(true));
+  xmpp_client_->Read();
+  EXPECT_EQ(TestHelper::GetState(*xmpp_client_),
+            XmppClient::XmppState::kStreamRestartedPostAuthentication);
+}
+
+TEST_F(XmppClientTest, HandleStreamRestartedResponse) {
+  TestHelper::SetState(
+      xmpp_client_.get(),
+      XmppClient::XmppState::kStreamRestartedPostAuthentication);
+  EXPECT_CALL(*connection_, Read(_))
+      .WillOnce(DoAll(SetArgPointee<0>(kRestartStreamResponse), Return(true)));
+  EXPECT_CALL(*connection_, Write(kBindMessage))
+      .WillOnce(Return(true));
+  xmpp_client_->Read();
+  EXPECT_EQ(TestHelper::GetState(*xmpp_client_),
+            XmppClient::XmppState::kBindSent);
+}
+
+TEST_F(XmppClientTest, HandleBindResponse) {
+  TestHelper::SetState(xmpp_client_.get(),
+                       XmppClient::XmppState::kBindSent);
+  EXPECT_CALL(*connection_, Read(_))
+      .WillOnce(DoAll(SetArgPointee<0>(kBindResponse), Return(true)));
+  EXPECT_CALL(*connection_, Write(kSessionMessage))
+      .WillOnce(Return(true));
+  xmpp_client_->Read();
+  EXPECT_EQ(TestHelper::GetState(*xmpp_client_),
+            XmppClient::XmppState::kSessionStarted);
+}
+
+TEST_F(XmppClientTest, HandleSessionResponse) {
+  TestHelper::SetState(xmpp_client_.get(),
+                       XmppClient::XmppState::kSessionStarted);
+  EXPECT_CALL(*connection_, Read(_))
+      .WillOnce(DoAll(SetArgPointee<0>(kSessionResponse), Return(true)));
+  EXPECT_CALL(*connection_, Write(kSubscribeMessage))
+      .WillOnce(Return(true));
+  xmpp_client_->Read();
+  EXPECT_EQ(TestHelper::GetState(*xmpp_client_),
+            XmppClient::XmppState::kSubscribeStarted);
+}
+
+TEST_F(XmppClientTest, HandleSubscribeResponse) {
+  TestHelper::SetState(xmpp_client_.get(),
+                       XmppClient::XmppState::kSubscribeStarted);
+  EXPECT_CALL(*connection_, Read(_))
+      .WillOnce(DoAll(SetArgPointee<0>(kSubscribedResponse), Return(true)));
+  EXPECT_CALL(*connection_, Write(_))
+      .Times(0);
+  xmpp_client_->Read();
+  EXPECT_EQ(TestHelper::GetState(*xmpp_client_),
+            XmppClient::XmppState::kSubscribed);
+}
+
+}  // namespace buffet