Introduce CryptAuthClient, a class capable of performing all CryptAuth APIs.

components/proximity_auth/cryptauth/cryptauth_client_unittest.cc

+// Copyright 2014 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 "components/proximity_auth/cryptauth/cryptauth_client.h"
+
+#include "base/command_line.h"
+#include "base/test/null_task_runner.h"
+#include "components/proximity_auth/cryptauth/cryptauth_access_token_fetcher.h"
+#include "components/proximity_auth/cryptauth/cryptauth_api_call_flow.h"
+#include "components/proximity_auth/cryptauth/proto/cryptauth_api.pb.h"
+#include "components/proximity_auth/switches.h"
+#include "net/url_request/test_url_fetcher_factory.h"
+#include "net/url_request/url_request_test_util.h"
+#include "testing/gmock/include/gmock/gmock.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+using testing::_;
+using testing::DoAll;
+using testing::Return;
+using testing::SaveArg;
+using testing::NiceMock;
+
+namespace proximity_auth {
+
+namespace {
+
+const char kTestGoogleApisUrl[] = "https://www.testgoogleapis.com";
+const char kAccessToken[] = "access_token";
+const char kPublicKey1[] = "public_key1";
+const char kPublicKey2[] = "public_key2";
+const char kBluetoothAddress1[] = "AA:AA:AA:AA:AA:AA";
+const char kBluetoothAddress2[] = "BB:BB:BB:BB:BB:BB";
+
+// CryptAuthAccessTokenFetcher implementation simply returning a predetermined
+// access token.
+class FakeCryptAuthAccessTokenFetcher : public CryptAuthAccessTokenFetcher {
+ public:
+  FakeCryptAuthAccessTokenFetcher() : access_token_(kAccessToken) {}
+
+  void FetchAccessToken(const AccessTokenCallback& callback) override {
+    callback.Run(access_token_);
+  }
+
+  void set_access_token(const std::string& access_token) {
+    access_token_ = access_token;
+  };
+
+ private:
+  std::string access_token_;
+};
+
+// Mock CryptAuthApiCallFlow, which handles the HTTP requests to CryptAuth.
+class MockCryptAuthApiCallFlow : public CryptAuthApiCallFlow {
+ public:
+  MockCryptAuthApiCallFlow() : CryptAuthApiCallFlow(GURL(std::string())) {}
+  virtual ~MockCryptAuthApiCallFlow() {}
+
+  MOCK_METHOD5(Start,
+               void(net::URLRequestContextGetter* context,
+                    const std::string& access_token,
+                    const std::string& serialized_request,
+                    ResultCallback result_callback,
+                    ErrorCallback error_callback));

[Ilya Sherman, 2014/12/03 03:16:37]

Hmm, how come the callbacks aren't passed by const-ref?

[Tim Song, 2014/12/05 00:00:36]

Done.

+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MockCryptAuthApiCallFlow);
+};
+
+// Subclass of CryptAuthClient to use as test harness.
+class MockCryptAuthClient : public CryptAuthClient {
+ public:
+  // Ownership of |access_token_fetcher| is passed to the superclass. Due to the
+  // limitations of gmock, we need to use a raw pointer argument rather than a
+  // scoped_ptr.

[Ilya Sherman, 2014/12/03 03:16:37]

Hmm, could you clarify how gmock is involved here?  I know that you can't used
scoped_ptrs in mocked methods, but what's the problem with using one in the
constructor?

[Tim Song, 2014/12/05 00:00:36]

It's for the same reason I think. The definition of Nice/StrictMock classes in
gmock-generated-nice-strict.h require const references for the templated
arguments passed to constructors. Because scoped_ptr::Pass() is not const, we
can't enforce correct ownership semantics. 

[Ilya Sherman, 2014/12/05 00:14:20]

Oh, I see, because we wrap this class in a NiceMock/StrictMock.  Makes sense.

+  MockCryptAuthClient(
+      CryptAuthAccessTokenFetcher* access_token_fetcher,
+      scoped_refptr<net::URLRequestContextGetter> url_request_context)
+      : CryptAuthClient(make_scoped_ptr(access_token_fetcher),
+                        url_request_context) {}
+  virtual ~MockCryptAuthClient() {}
+
+  MOCK_METHOD1(CreateFlow, CryptAuthApiCallFlow*(const GURL& request_url));

[Ilya Sherman, 2014/12/03 03:16:37]

I'm wondering if the reason you made CreateFlow return a non-scoped_ptr is so
that you could mock the method.  If so, I'd prefer that you create a "wrapper"
method that's mocked, as I've done in other tests -- the needs of test code
shouldn't reduce the clarity of production code, wherever possible.

[Tim Song, 2014/12/05 00:00:36]

Done.

+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MockCryptAuthClient);
+};
+
+// Callback that should never be invoked.
+template <class T>
+void NotCalled(const T& type) {
+  EXPECT_TRUE(false);
+}
+
+// Callback that saves the result returned by CryptAuthClient.
+template <class T>
+void SaveResult(T* out, const T& result) {
+  // static assert

[Ilya Sherman, 2014/12/03 03:16:37]

I don't follow what this comment means -- could you clarify?

[Tim Song, 2014/12/05 00:00:36]

Sorry, that comment was accidentally left in.

+  *out = result;
+}
+
+}  // namespace
+
+class ProximityAuthCryptAuthClientTest : public testing::Test {
+ protected:
+  ProximityAuthCryptAuthClientTest()
+      : access_token_fetcher_(new FakeCryptAuthAccessTokenFetcher()),
+        url_request_context_(
+            new net::TestURLRequestContextGetter(new base::NullTaskRunner())),
+        serialized_request_("") {}

[Ilya Sherman, 2014/12/03 03:16:37]

nit: Please prefer std::string() to "".

[Tim Song, 2014/12/05 00:00:36]

Done.

+  virtual ~ProximityAuthCryptAuthClientTest() {}
+
+  void SetUp() override {
+    base::CommandLine::ForCurrentProcess()->AppendSwitchASCII(
+        switches::kCryptAuthHTTPHost, kTestGoogleApisUrl);
+
+    client_.reset(new NiceMock<MockCryptAuthClient>(access_token_fetcher_,

[Ilya Sherman, 2014/12/03 03:16:37]

nit: Any reason not to use a StrictMock?  Are there calls to CreateFlow that
some tests aren't interested in?

[Tim Song, 2014/12/05 00:00:36]

Done.

+                                                    url_request_context_));
+  }
+
+  // Sets up an expectation and captures a CryptAuth API request to
+  // |request_url|.
+  void ExpectRequest(const std::string& request_url) {
+    NiceMock<MockCryptAuthApiCallFlow>* api_call_flow =
+        new NiceMock<MockCryptAuthApiCallFlow>();
+
+    EXPECT_CALL(*client_, CreateFlow(GURL(request_url)))
+        .WillOnce(Return(api_call_flow));
+
+    EXPECT_CALL(*api_call_flow,
+                Start(url_request_context_.get(), kAccessToken, _, _, _))
+        .WillOnce(DoAll(SaveArg<2>(&serialized_request_),
+                        SaveArg<3>(&flow_result_callback_),
+                        SaveArg<4>(&flow_error_callback_)));
+  }
+
+  // Returns |response_proto| as the result to the current API request.
+  // ExpectResult() must have been called first.
+  void FinishApiCallFlow(const google::protobuf::MessageLite* response_proto) {
+    std::string serialized_proto;
+    response_proto->SerializeToString(&serialized_proto);

[Ilya Sherman, 2014/12/03 03:16:37]

nit: I think you can use "SerializeAsString" to save a line or two of code.

[Tim Song, 2014/12/05 00:00:36]

Done.

+    flow_result_callback_.Run(serialized_proto);
+  }
+
+  // Ends the current API request with |error_message|. ExpectResult() must have
+  // been called first.
+  void FailApiCallFlow(const std::string& error_message) {
+    flow_error_callback_.Run(error_message);
+  }
+
+ protected:
+  // Owned by |client_|.
+  FakeCryptAuthAccessTokenFetcher* access_token_fetcher_;
+
+  scoped_refptr<net::URLRequestContextGetter> url_request_context_;
+  scoped_ptr<NiceMock<MockCryptAuthClient>> client_;
+
+  std::string serialized_request_;
+  CryptAuthApiCallFlow::ResultCallback flow_result_callback_;
+  CryptAuthApiCallFlow::ErrorCallback flow_error_callback_;
+};
+
+TEST_F(ProximityAuthCryptAuthClientTest, GetMyDevicesSuccess) {
+  ExpectRequest(
+      "https://www.testgoogleapis.com/cryptauth/v1/deviceSync/"
+      "getmydevices?alt=proto");
+
+  cryptauth::GetMyDevicesResponse result_proto;
+  cryptauth::GetMyDevicesRequest request_proto;
+  request_proto.set_allow_stale_read(true);
+  client_->GetMyDevices(
+      request_proto,
+      base::Bind(&SaveResult<cryptauth::GetMyDevicesResponse>, &result_proto),
+      base::Bind(&NotCalled<std::string>));
+
+  cryptauth::GetMyDevicesRequest expected_request;
+  EXPECT_TRUE(expected_request.ParseFromString(serialized_request_));
+  EXPECT_TRUE(expected_request.allow_stale_read());
+
+  // Return two devices, one unlock key and one unlockable device.
+  {
+    cryptauth::GetMyDevicesResponse response_proto;
+    response_proto.add_devices();
+    response_proto.mutable_devices(0)->set_public_key(kPublicKey1);
+    response_proto.mutable_devices(0)->set_unlock_key(true);
+    response_proto.mutable_devices(0)
+        ->set_bluetooth_address(kBluetoothAddress1);
+    response_proto.add_devices();
+    response_proto.mutable_devices(1)->set_public_key(kPublicKey2);
+    response_proto.mutable_devices(1)->set_unlockable(true);
+    FinishApiCallFlow(&response_proto);
+  }
+
+  // Check that the result received in callback is the same as the response.
+  ASSERT_EQ(2, result_proto.devices_size());
+  EXPECT_EQ(kPublicKey1, result_proto.devices(0).public_key());
+  EXPECT_TRUE(result_proto.devices(0).unlock_key());
+  EXPECT_EQ(kBluetoothAddress1, result_proto.devices(0).bluetooth_address());
+  EXPECT_EQ(kPublicKey2, result_proto.devices(1).public_key());
+  EXPECT_TRUE(result_proto.devices(1).unlockable());
+}
+
+TEST_F(ProximityAuthCryptAuthClientTest, GetMyDevicesFailure) {
+  ExpectRequest(
+      "https://www.testgoogleapis.com/cryptauth/v1/deviceSync/"
+      "getmydevices?alt=proto");
+
+  std::string error_message;
+  client_->GetMyDevices(cryptauth::GetMyDevicesRequest(),
+                        base::Bind(&NotCalled<cryptauth::GetMyDevicesResponse>),
+                        base::Bind(&SaveResult<std::string>, &error_message));
+
+  std::string kStatus500Error("HTTP status: 500");
+  FailApiCallFlow(kStatus500Error);
+  EXPECT_EQ(kStatus500Error, error_message);
+}
+
+TEST_F(ProximityAuthCryptAuthClientTest, FindEligibleUnlockDevicesSuccess) {
+  ExpectRequest(
+      "https://www.testgoogleapis.com/cryptauth/v1/deviceSync/"
+      "findeligibleunlockdevices?alt=proto");
+
+  cryptauth::FindEligibleUnlockDevicesResponse result_proto;
+  cryptauth::FindEligibleUnlockDevicesRequest request_proto;
+  request_proto.set_callback_bluetooth_address(kBluetoothAddress2);
+  client_->FindEligibleUnlockDevices(
+      request_proto,
+      base::Bind(&SaveResult<cryptauth::FindEligibleUnlockDevicesResponse>,
+                 &result_proto),
+      base::Bind(&NotCalled<std::string>));
+
+  cryptauth::FindEligibleUnlockDevicesRequest expected_request;
+  EXPECT_TRUE(expected_request.ParseFromString(serialized_request_));
+  EXPECT_EQ(kBluetoothAddress2, expected_request.callback_bluetooth_address());
+
+  // Return a response proto with one eligible and one ineligible device.
+  cryptauth::FindEligibleUnlockDevicesResponse response_proto;
+  response_proto.add_eligible_devices();
+  response_proto.mutable_eligible_devices(0)->set_public_key(kPublicKey1);
+
+  const std::string kIneligibilityReason = "You require more vespine gas.";

[Ilya Sherman, 2014/12/03 03:16:37]

:)

+  response_proto.add_ineligible_devices();
+  response_proto.mutable_ineligible_devices(0)
+      ->mutable_device()
+      ->set_public_key(kPublicKey2);
+  response_proto.mutable_ineligible_devices(0)
+      ->add_reasons(kIneligibilityReason);
+  FinishApiCallFlow(&response_proto);
+
+  // Check that the result received in callback is the same as the response.
+  ASSERT_EQ(1, result_proto.eligible_devices_size());
+  EXPECT_EQ(kPublicKey1, result_proto.eligible_devices(0).public_key());
+  ASSERT_EQ(1, result_proto.ineligible_devices_size());
+  EXPECT_EQ(kPublicKey2,
+            result_proto.ineligible_devices(0).device().public_key());
+  ASSERT_EQ(1, result_proto.ineligible_devices(0).reasons_size());
+  EXPECT_EQ(kIneligibilityReason,
+            result_proto.ineligible_devices(0).reasons(0));
+}
+
+TEST_F(ProximityAuthCryptAuthClientTest, FindEligibleUnlockDevicesFailure) {
+  ExpectRequest(
+      "https://www.testgoogleapis.com/cryptauth/v1/deviceSync/"
+      "findeligibleunlockdevices?alt=proto");
+
+  std::string error_message;
+  cryptauth::FindEligibleUnlockDevicesRequest request_proto;
+  request_proto.set_callback_bluetooth_address(kBluetoothAddress1);
+  client_->FindEligibleUnlockDevices(
+      request_proto,
+      base::Bind(&NotCalled<cryptauth::FindEligibleUnlockDevicesResponse>),
+      base::Bind(&SaveResult<std::string>, &error_message));
+
+  std::string kStatus403Error("HTTP status: 403");
+  FailApiCallFlow(kStatus403Error);
+  EXPECT_EQ(kStatus403Error, error_message);
+}
+
+TEST_F(ProximityAuthCryptAuthClientTest, SendDeviceSyncTickleSuccess) {
+  ExpectRequest(
+      "https://www.testgoogleapis.com/cryptauth/v1/deviceSync/"
+      "senddevicesynctickle?alt=proto");
+
+  cryptauth::SendDeviceSyncTickleResponse result_proto;
+  client_->SendDeviceSyncTickle(
+      cryptauth::SendDeviceSyncTickleRequest(),
+      base::Bind(&SaveResult<cryptauth::SendDeviceSyncTickleResponse>,
+                 &result_proto),
+      base::Bind(&NotCalled<std::string>));
+
+  cryptauth::SendDeviceSyncTickleRequest expected_request;
+  EXPECT_TRUE(expected_request.ParseFromString(serialized_request_));
+
+  cryptauth::SendDeviceSyncTickleResponse response_proto;
+  FinishApiCallFlow(&response_proto);
+}
+
+TEST_F(ProximityAuthCryptAuthClientTest, ToggleEasyUnlockSuccess) {
+  ExpectRequest(
+      "https://www.testgoogleapis.com/cryptauth/v1/deviceSync/"
+      "toggleeasyunlock?alt=proto");
+
+  cryptauth::ToggleEasyUnlockResponse result_proto;
+  cryptauth::ToggleEasyUnlockRequest request_proto;
+  request_proto.set_enable(true);
+  request_proto.set_apply_to_all(false);
+  request_proto.set_public_key(kPublicKey1);
+  client_->ToggleEasyUnlock(
+      request_proto,
+      base::Bind(&SaveResult<cryptauth::ToggleEasyUnlockResponse>,
+                 &result_proto),
+      base::Bind(&NotCalled<std::string>));
+
+  cryptauth::ToggleEasyUnlockRequest expected_request;
+  EXPECT_TRUE(expected_request.ParseFromString(serialized_request_));
+  EXPECT_TRUE(expected_request.enable());
+  EXPECT_EQ(kPublicKey1, expected_request.public_key());
+  EXPECT_FALSE(expected_request.apply_to_all());
+
+  cryptauth::ToggleEasyUnlockResponse response_proto;
+  FinishApiCallFlow(&response_proto);
+}
+
+TEST_F(ProximityAuthCryptAuthClientTest, SetupEnrollmentSuccess) {
+  ExpectRequest(
+      "https://www.testgoogleapis.com/cryptauth/v1/enrollment/"
+      "setupenrollment?alt=proto");
+
+  std::string kApplicationId = "mkaes";
+  std::vector<std::string> supported_protocols;
+  supported_protocols.push_back("gcmV1");
+  supported_protocols.push_back("testProtocol");
+
+  cryptauth::SetupEnrollmentResponse result_proto;
+  cryptauth::SetupEnrollmentRequest request_proto;
+  request_proto.set_application_id(kApplicationId);
+  request_proto.add_types("gcmV1");
+  request_proto.add_types("testProtocol");
+  client_->SetupEnrollment(
+      request_proto, base::Bind(&SaveResult<cryptauth::SetupEnrollmentResponse>,
+                                &result_proto),
+      base::Bind(&NotCalled<std::string>));
+
+  cryptauth::SetupEnrollmentRequest expected_request;
+  EXPECT_TRUE(expected_request.ParseFromString(serialized_request_));
+  EXPECT_EQ(kApplicationId, expected_request.application_id());
+  ASSERT_EQ(2, expected_request.types_size());
+  EXPECT_EQ("gcmV1", expected_request.types(0));
+  EXPECT_EQ("testProtocol", expected_request.types(1));
+
+  // Return a fake enrollment session.
+  {
+    cryptauth::SetupEnrollmentResponse response_proto;
+    response_proto.set_status("OK");
+    response_proto.add_infos();
+    response_proto.mutable_infos(0)->set_type("gcmV1");
+    response_proto.mutable_infos(0)->set_enrollment_session_id("session_id");
+    response_proto.mutable_infos(0)->set_server_ephemeral_key("ephemeral_key");
+    FinishApiCallFlow(&response_proto);
+  }
+
+  // Check that the returned proto is the same as the one just created.
+  EXPECT_EQ("OK", result_proto.status());
+  ASSERT_EQ(1, result_proto.infos_size());
+  EXPECT_EQ("gcmV1", result_proto.infos(0).type());
+  EXPECT_EQ("session_id", result_proto.infos(0).enrollment_session_id());
+  EXPECT_EQ("ephemeral_key", result_proto.infos(0).server_ephemeral_key());
+}
+
+TEST_F(ProximityAuthCryptAuthClientTest, FinishEnrollmentSuccess) {
+  ExpectRequest(
+      "https://www.testgoogleapis.com/cryptauth/v1/enrollment/"
+      "finishenrollment?alt=proto");
+
+  const char kEnrollmentSessionId[] = "enrollment_session_id";
+  const char kEnrollmentMessage[] = "enrollment_message";
+  const char kDeviceEphemeralKey[] = "device_ephermal_key";
+  cryptauth::FinishEnrollmentResponse result_proto;
+  cryptauth::FinishEnrollmentRequest request_proto;
+  request_proto.set_enrollment_session_id(kEnrollmentSessionId);
+  request_proto.set_enrollment_message(kEnrollmentMessage);
+  request_proto.set_device_ephemeral_key(kDeviceEphemeralKey);
+  client_->FinishEnrollment(
+      request_proto,
+      base::Bind(&SaveResult<cryptauth::FinishEnrollmentResponse>,
+                 &result_proto),
+      base::Bind(&NotCalled<const std::string&>));
+
+  cryptauth::FinishEnrollmentRequest expected_request;
+  EXPECT_TRUE(expected_request.ParseFromString(serialized_request_));
+  EXPECT_EQ(kEnrollmentSessionId, expected_request.enrollment_session_id());
+  EXPECT_EQ(kEnrollmentMessage, expected_request.enrollment_message());
+  EXPECT_EQ(kDeviceEphemeralKey, expected_request.device_ephemeral_key());
+
+  {
+    cryptauth::FinishEnrollmentResponse response_proto;
+    response_proto.set_status("OK");
+    FinishApiCallFlow(&response_proto);
+  }
+  EXPECT_EQ("OK", result_proto.status());
+}
+
+TEST_F(ProximityAuthCryptAuthClientTest, FetchAccessTokenFailure) {
+  access_token_fetcher_->set_access_token("");
+
+  std::string error_message;
+  client_->GetMyDevices(cryptauth::GetMyDevicesRequest(),
+                        base::Bind(&NotCalled<cryptauth::GetMyDevicesResponse>),
+                        base::Bind(&SaveResult<std::string>, &error_message));
+
+  EXPECT_EQ("Failed to get a valid access token", error_message);
+}
+
+TEST_F(ProximityAuthCryptAuthClientTest,
+       MakeSecondRequestBeforeFirstRequestSucceeds) {
+  ExpectRequest(
+      "https://www.testgoogleapis.com/cryptauth/v1/deviceSync/"
+      "getmydevices?alt=proto");
+
+  // Make first request.
+  cryptauth::GetMyDevicesResponse result_proto;
+  client_->GetMyDevices(
+      cryptauth::GetMyDevicesRequest(),
+      base::Bind(&SaveResult<cryptauth::GetMyDevicesResponse>, &result_proto),
+      base::Bind(&NotCalled<std::string>));
+
+  // With request pending, make second request.
+  {
+    std::string error_message;
+    client_->FindEligibleUnlockDevices(
+        cryptauth::FindEligibleUnlockDevicesRequest(),
+        base::Bind(&NotCalled<cryptauth::FindEligibleUnlockDevicesResponse>),
+        base::Bind(&SaveResult<std::string>, &error_message));
+    EXPECT_EQ("Client has been used for another request. Do not reuse.",
+              error_message);
+  }
+
+  // Complete first request.
+  {
+    cryptauth::GetMyDevicesResponse response_proto;
+    response_proto.add_devices();
+    response_proto.mutable_devices(0)->set_public_key(kPublicKey1);
+    FinishApiCallFlow(&response_proto);
+  }
+
+  ASSERT_EQ(1, result_proto.devices_size());
+  EXPECT_EQ(kPublicKey1, result_proto.devices(0).public_key());
+}
+
+TEST_F(ProximityAuthCryptAuthClientTest,
+       MakeSecondRequestBeforeFirstRequestFails) {
+  ExpectRequest(
+      "https://www.testgoogleapis.com/cryptauth/v1/deviceSync/"
+      "getmydevices?alt=proto");
+
+  // Make first request.
+  std::string error_message;
+  client_->GetMyDevices(cryptauth::GetMyDevicesRequest(),
+                        base::Bind(&NotCalled<cryptauth::GetMyDevicesResponse>),
+                        base::Bind(&SaveResult<std::string>, &error_message));
+
+  // With request pending, make second request.
+  {
+    std::string error_message;
+    client_->FindEligibleUnlockDevices(
+        cryptauth::FindEligibleUnlockDevicesRequest(),
+        base::Bind(&NotCalled<cryptauth::FindEligibleUnlockDevicesResponse>),
+        base::Bind(&SaveResult<std::string>, &error_message));
+    EXPECT_EQ("Client has been used for another request. Do not reuse.",
+              error_message);
+  }
+
+  // Fail first request.
+  std::string kStatus429Error = "HTTP status: 429";
+  FailApiCallFlow(kStatus429Error);
+  EXPECT_EQ(kStatus429Error, error_message);
+}
+
+TEST_F(ProximityAuthCryptAuthClientTest,
+       MakeSecondRequestAfterFirstRequestSucceeds) {
+  // Make first request successfully.
+  {
+    ExpectRequest(
+        "https://www.testgoogleapis.com/cryptauth/v1/deviceSync/"
+        "getmydevices?alt=proto");
+    cryptauth::GetMyDevicesResponse result_proto;
+    client_->GetMyDevices(
+        cryptauth::GetMyDevicesRequest(),
+        base::Bind(&SaveResult<cryptauth::GetMyDevicesResponse>, &result_proto),
+        base::Bind(&NotCalled<std::string>));
+
+    cryptauth::GetMyDevicesResponse response_proto;
+    response_proto.add_devices();
+    response_proto.mutable_devices(0)->set_public_key(kPublicKey1);
+    FinishApiCallFlow(&response_proto);
+    ASSERT_EQ(1, result_proto.devices_size());
+    EXPECT_EQ(kPublicKey1, result_proto.devices(0).public_key());
+  }
+
+  // Second request fails.
+  {
+    std::string error_message;
+    client_->FindEligibleUnlockDevices(
+        cryptauth::FindEligibleUnlockDevicesRequest(),
+        base::Bind(&NotCalled<cryptauth::FindEligibleUnlockDevicesResponse>),
+        base::Bind(&SaveResult<std::string>, &error_message));
+    EXPECT_EQ("Client has been used for another request. Do not reuse.",
+              error_message);
+  }
+}
+
+}  // namespace proximity_auth