Testing your Cloud Pub/Sub publisher application with googlemock

This document describes how to test your own Cloud Pub/Sub application using the Cloud Pub/Sub C++ client library, Google Test and the and Google Test Mocking Framework.

Mocking a Successful Publisher::Publish() call

First include the headers for the Cloud Pub/Sub Publisher Client, the mocking class, and the Google Mock framework.

#include "google/cloud/pubsub/mocks/mock_publisher_connection.h"
#include "google/cloud/pubsub/publisher.h"
#include <gmock/gmock.h>

The example uses a number of aliases to save typing and improve readability:

using ::google::cloud::pubsub_mocks::MockPublisherConnection;
namespace pubsub = ::google::cloud::pubsub;

Create a mocking object for google::cloud::pubsub::PublisherConnection:

  auto mock = std::make_shared<MockPublisherConnection>();

It is customary to first setup the expectations for your mock, and then write the rest of the code:

  EXPECT_CALL(*mock, Publish)
      .WillOnce([&](pubsub::PublisherConnection::PublishParams const& p) {
        EXPECT_EQ("test-data-0", p.message.data());
        return google::cloud::make_ready_future(
            google::cloud::StatusOr<std::string>("test-id-0"));
      });

With the expectations in place, create a google::cloud::pubsub::Publisher object:

  pubsub::Publisher publisher(mock);

And then make calls on the client as usual:

  auto id =
      publisher.Publish(pubsub::MessageBuilder{}.SetData("test-data-0").Build())
          .get();

And then verify the results meet your expectations:

  EXPECT_TRUE(id.ok());
  EXPECT_EQ("test-id-0", *id);

Full Listing

Finally we present the full code for this example:

 
#include "google/cloud/pubsub/mocks/mock_publisher_connection.h"
#include "google/cloud/pubsub/publisher.h"
#include <gmock/gmock.h>
 
namespace {
 
using ::google::cloud::pubsub_mocks::MockPublisherConnection;
namespace pubsub = ::google::cloud::pubsub;
 
TEST(MockPublishExample, PublishSimple) {
  auto mock = std::make_shared<MockPublisherConnection>();
 
  EXPECT_CALL(*mock, Publish)
      .WillOnce([&](pubsub::PublisherConnection::PublishParams const& p) {
        EXPECT_EQ("test-data-0", p.message.data());
        return google::cloud::make_ready_future(
            google::cloud::StatusOr<std::string>("test-id-0"));
      });
 
  pubsub::Publisher publisher(mock);
 
  auto id =
      publisher.Publish(pubsub::MessageBuilder{}.SetData("test-data-0").Build())
          .get();
 
  EXPECT_TRUE(id.ok());
  EXPECT_EQ("test-id-0", *id);
}
 
}  // namespace