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