There are a lot of information in the title I know, but I am not good enough to make it simple.

Back in the days, I tried to make some contribution to OpenZipkin an open source tracing infrastructure in Java. I never really worked in that language, and apparently, I failed, but it wasn’t all a waste of time.

OpenZipkin has an excellent integration test suite, and I liked the approach it took to write integration tests for all the backends it supports MySql, ElasticSeach, Cassandra.

Provision the integration test environment is complicated even when you do it wrong:

Without a per test isolation. Without a cleanup process. Without putting the right effort to have isolated tests.

If you try to make integration tests in the right way, you will have a very hard time, but Zipkin uses a project called testcontainers-java. It is a library that wraps the Docker SDK to offer a friendly API to write integration tests using containers.

Why containers

In 2019 everyone knows the answer, containers are great for integration testings because they are a lightweight and flexible technology. Docker provides the architecture that simplifies how you can turn them on and off.

You can spin up a bunch of containers for every integration tests, they will be fresh new, and you can terminate them at the end of the tests. This increases isolation a lot, and it makes your tests more stable and easy to reproduce.

Golang

I develop in Go every day I loved the approach, so I decided to port that library to Golang and it eventually get moved to the testcontainers GitHub organization under the repository testcontainers/testcontainers-go.

There is a lot to do but I think at this point the API is stable and we have everything we need to use it. All the rest will be driven by yourself asking for new features or from contributors that will port more things from the java project.

This is our “Hello World.”

package main import ( "context" "fmt" "net/http" "testing" testcontainers "github.com/testcontainers/testcontainers-go" ) // TestNginxLatestReturn verifies that a requesto to root returns 200 as status // code func TestNginxLatestReturn ( t * testing . T ) { ctx := context . Background () // Request an nginx container that exposes port 80 req := testcontainers . ContainerRequest { Image : "nginx" , ExposedPorts : [] string { "80/tcp" }, } nginxC , err := testcontainers . GenericContainer ( ctx , testcontainers . GenericContainerRequest { ContainerRequest : req , Started : true , }) if err != nil { t . Error ( err ) } // At the end of the test remove the container defer nginxC . Terminate ( ctx ) // Retrieve the container IP ip , err := nginxC . Host ( ctx ) if err != nil { t . Error ( err ) } // Retrieve the port mapped to port 80 port , err := nginxC . MappedPort ( ctx , "80" ) if err != nil { t . Error ( err ) } resp , err := http . Get ( fmt . Sprintf ( "http://%s:%s" , ip , port . Port ())) if resp . StatusCode != http . StatusOK { t . Errorf ( "Expected status code %d. Got %d." , http . StatusOK , resp . StatusCode ) } }

This is a straightforward test, but you can imagine a lot of other use cases. Let’s say that you need to test how your application A interact with an application B that depends on Redis. You can programmatically build the environment you need in the tests:

// You spin up the Redis container req := testcontainers.ContainerRequest{ Image: "redis", ExposedPorts: []string{"6379/tcp"}, } redisC, err := testcontainers.GenericContainer(ctx, testcontainers.GenericContainerRequest{ ContainerRequest: req, Started: true, }) if err != nil { t.Error(err) } defer redisC.Terminate(ctx) ip, err := redisC.Host(ctx) if err != nil { t.Error(err) } redisPort, err := redisC.MappedPort(ctx, "6479/tcp") if err != nil { t.Error(err) } // Spin up Application B appB, err := testcontainers.GenericContainer(ctx, testcontainers.GenericContainerRequest{ ContainerRequest: req, Started: true, Env: map[string]string{ "REDIS_HOST": fmt.Sprintf("http://%s:%s", ip, redisPort.Port()), }, }) if err != nil { t.Error(err) } ipB, err := redisC.Host(ctx) if err != nil { t.Error(err) } portB, err := redisC.MappedPort(ctx, "8081/tcp") if err != nil { t.Error(err) } defer appB.Terminate(ctx) defer redis.Terminate(ctx) // Now you can use the go function from your application A that interact with // application B bclient := appA.NewServiceBClient(ipB, portB) content, err := bclient.GetKey("my-key") // Check what you need to check

Programmable environment is the key

I wrote about my relationship with infrastructure as code in a previous article but once again the fact that you can programmatically build your infrastructure using real code is the key for all this flexibility.

As plus for integration tests, you can build the environment you need from inside the test case itself, this ability provides significant control over it.

If you need to worm up etcd with some data, you spin up the etcd container and you push your data using the traditional Go etcd client:

// Spin up Etcd req := testcontainers.ContainerRequest{ Image: "quay.io/coreos/etcd:latest", ExposedPorts: []string{"2379/tcp"}, } etcdC, err := testcontainers.GenericContainer(ctx, testcontainers.GenericContainerRequest{ ContainerRequest: req, Started: true, }) if err != nil { t.Error(err) } defer etcdC.Terminate(ctx) ip, err := etcdC.Host(ctx) if err != nil { t.Error(err) } etcdPort, err := redisC.MappedPort(ctx, "2379/tcp") if err != nil { t.Error(err) } // Configure the etcd client cfg := client.Config{ Endpoints: []string{"http://" + ip + ":" + etcdPort}, Transport: client.DefaultTransport, // set timeout per request to fail fast when the target endpoint is unavailable HeaderTimeoutPerRequest: time.Second, } c, err := client.New(cfg) if err != nil { log.Fatal(err) } kapi := client.NewKeysAPI(c) // Set the key foo resp, err := kapi.Set(context.Background(), "/foo", "bar", nil)