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K6

Since testcontainers-go v0.26.0

Introduction

The Testcontainers module for K6.

Using k6 extensions

This module takes advantage of k6x to dynamically build a k6 binary with all the k6 extensions required by the test script.

Adding this module to your project dependencies

Please run the following command to add the K6 module to your Go dependencies:

go get github.com/testcontainers/testcontainers-go/modules/k6

Usage example

ctx := context.Background()

// create a container with the httpbin application that will be the target
// for the test script that runs in the k6 container
gcr := testcontainers.GenericContainerRequest{
    ProviderType: testcontainers.ProviderDocker,
    ContainerRequest: testcontainers.ContainerRequest{
        Image: "kennethreitz/httpbin",
        ExposedPorts: []string{
            "80",
        },
        WaitingFor: wait.ForExposedPort(),
    },
    Started: true,
}
httpbin, err := testcontainers.GenericContainer(ctx, gcr)
if err != nil {
    log.Fatalf("failed to start container: %s", err)
}

defer func() {
    if err := httpbin.Terminate(ctx); err != nil {
        log.Fatalf("failed to terminate container: %s", err)
    }
}()

httpbinIP, err := httpbin.ContainerIP(ctx)
if err != nil {
    log.Fatalf("failed to get container IP: %s", err) // nolint:gocritic
}

import { check } from 'k6';
import http from 'k6/http';

export default function () {
  const res = http.get(`http://${__ENV.HTTPBIN}/status/200`);

  check(res, {
    'is status 200': (r) => r.status === 200,
  });
}

// run the httpbin.js test scripts passing the IP address the httpbin container
k6, err := k6.RunContainer(
    ctx,
    k6.WithCache(),
    k6.WithTestScript(absPath),
    k6.SetEnvVar("HTTPBIN", httpbinIP),
)
if err != nil {
    log.Fatalf("failed to start container: %s", err)
}

defer func() {
    if err := k6.Terminate(ctx); err != nil {
        log.Fatalf("failed to terminate container: %s", err)
    }
}()

Module reference

The K6 module exposes one entrypoint function to run the K6 container, and this function receives two parameters:

func RunContainer(ctx context.Context, opts ...testcontainers.ContainerCustomizer) (*K6Container, error)
  • context.Context, the Go context.
  • testcontainers.ContainerCustomizer, a variadic argument for passing options.

Container Options

When starting the K6 container, you can pass options in a variadic way to configure it.

Image

Warning

The K6 module uses a k6x image to build a k6 binary with all the required extensions. Therefore, only the szkiba/k6x image should be used with this module.

If you need to set a different K6 Docker image, you can use testcontainers.WithImage with a valid Docker image for k6x. E.g. testcontainers.WithImage("szkiba/k6x:v0.3.1").

Image Substitutions

In more locked down / secured environments, it can be problematic to pull images from Docker Hub and run them without additional precautions.

An image name substitutor converts a Docker image name, as may be specified in code, to an alternative name. This is intended to provide a way to override image names, for example to enforce pulling of images from a private registry.

Testcontainers for Go exposes an interface to perform this operations: ImageSubstitutor, and a No-operation implementation to be used as reference for custom implementations:

// ImageSubstitutor represents a way to substitute container image names
type ImageSubstitutor interface {
    // Description returns the name of the type and a short description of how it modifies the image.
    // Useful to be printed in logs
    Description() string
    Substitute(image string) (string, error)
}

type NoopImageSubstitutor struct{}

// Description returns a description of what is expected from this Substitutor,
// which is used in logs.
func (s NoopImageSubstitutor) Description() string {
    return "NoopImageSubstitutor (noop)"
}

// Substitute returns the original image, without any change
func (s NoopImageSubstitutor) Substitute(image string) (string, error) {
    return image, nil
}

Using the WithImageSubstitutors options, you could define your own substitutions to the container images. E.g. adding a prefix to the images so that they can be pulled from a Docker registry other than Docker Hub. This is the usual mechanism for using Docker image proxies, caches, etc.

WithEnv

If you need to either pass additional environment variables to a container or override them, you can use testcontainers.WithEnv for example:

postgres, err = postgresModule.RunContainer(ctx, testcontainers.WithEnv(map[string]string{"POSTGRES_INITDB_ARGS": "--no-sync"}))

WithHostPortAccess

If you need to access a port that is already running in the host, you can use testcontainers.WithHostPortAccess for example:

postgres, err = postgresModule.RunContainer(ctx, testcontainers.WithHostPortAccess(8080))

To understand more about this feature, please read the Exposing host ports to the container documentation.

WithLogConsumers

If you need to consume the logs of the container, you can use testcontainers.WithLogConsumers with a valid log consumer. An example of a log consumer is the following:

type TestLogConsumer struct {
    Msgs []string
}

func (g *TestLogConsumer) Accept(l Log) {
    g.Msgs = append(g.Msgs, string(l.Content))
}

WithLogger

If you need to either pass logger to a container, you can use testcontainers.WithLogger.

Info

Consider calling this before other "With" functions as these may generate logs.

In this example we also use TestLogger which writes to the passed in testing.TB using Logf. The result is that we capture all logging from the container into the test context meaning its hidden behind go test -v and is associated with the relevant test, providing the user with useful context instead of appearing out of band.

func TestHandler(t *testing.T) {
    logger := TestLogger(t)
    _, err := postgresModule.RunContainer(ctx, testcontainers.WithLogger(logger))
    require.NoError(t, err)
    // Do something with container.
}

Please read the Following Container Logs documentation for more information about creating log consumers.

Wait Strategies

If you need to set a different wait strategy for the container, you can use testcontainers.WithWaitStrategy with a valid wait strategy.

Info

The default deadline for the wait strategy is 60 seconds.

At the same time, it's possible to set a wait strategy and a custom deadline with testcontainers.WithWaitStrategyAndDeadline.

Startup Commands

Testcontainers exposes the WithStartupCommand(e ...Executable) option to run arbitrary commands in the container right after it's started.

Info

To better understand how this feature works, please read the Create containers: Lifecycle Hooks documentation.

It also exports an Executable interface, defining the following methods:

  • AsCommand(), which returns a slice of strings to represent the command and positional arguments to be executed in the container;
  • Options(), which returns the slice of functional options with the Docker's ExecConfigs used to create the command in the container (the working directory, environment variables, user executing the command, etc) and the possible output format (Multiplexed).

You could use this feature to run a custom script, or to run a command that is not supported by the module right after the container is started.

Ready Commands

Testcontainers exposes the WithAfterReadyCommand(e ...Executable) option to run arbitrary commands in the container right after it's ready, which happens when the defined wait strategies have finished with success.

Info

To better understand how this feature works, please read the Create containers: Lifecycle Hooks documentation.

It leverages the Executable interface to represent the command and positional arguments to be executed in the container.

You could use this feature to run a custom script, or to run a command that is not supported by the module right after the container is ready.

WithNetwork

By default, the container is started in the default Docker network. If you want to use an already existing Docker network you created in your code, you can use the network.WithNetwork(aliases []string, nw *testcontainers.DockerNetwork) option, which receives an alias as parameter and your network, attaching the container to it, and setting the network alias for that network.

In the case you need to retrieve the network name, you can simply read it from the struct's Name field. E.g. nw.Name.

Warning

This option is not checking whether the network exists or not. If you use a network that doesn't exist, the container will start in the default Docker network, as in the default behavior.

WithNewNetwork

If you want to attach your containers to a throw-away network, you can use the network.WithNewNetwork(ctx context.Context, aliases []string, opts ...network.NetworkCustomizer) option, which receives an alias as parameter, creating the new network with a random name, attaching the container to it, and setting the network alias for that network.

In the case you need to retrieve the network name, you can use the Networks(ctx) method of the Container interface, right after it's running, which returns a slice of strings with the names of the networks where the container is attached.

Docker type modifiers

If you need an advanced configuration for the container, you can leverage the following Docker type modifiers:

  • testcontainers.WithConfigModifier
  • testcontainers.WithHostConfigModifier
  • testcontainers.WithEndpointSettingsModifier

Please read the Create containers: Advanced Settings documentation for more information.

Customising the ContainerRequest

This option will merge the customized request into the module's own ContainerRequest.

container, err := RunContainer(ctx,
    /* Other module options */
    testcontainers.CustomizeRequest(testcontainers.GenericContainerRequest{
        ContainerRequest: testcontainers.ContainerRequest{
            Cmd: []string{"-c", "log_statement=all"},
        },
    }),
)

The above example is updating the predefined command of the image, appending them to the module's command.

Info

This can't be used to replace the command, only to append options.

SetEnvVar

SetEnvVar sets an environment variable for the test script using the '--env' command-line flag in the k6 command in the container.

k6.RunContainer(ctx, k6.SetEnvVar("URL","test.k6.io"), k6.WithTestScript("/tests/test.js"))

WithCache

Use WithCache sets a volume to be used as cache for building the k6 binary inside the k6 container. This option improves considerably the execution time of test suites that creates multiple k6 test containers.

By default, a new volume is created and automatically removed when the test session ends.

This is convenient for example for CI/CD environments. In other cases, such as local testing, it can be convenient to reuse the same cache volume across test sessions.In this cases, the TC_K6_BUILD_CACHE environment variables can used to provide the name of a volume to be used and kept across test sessions. If this volume does not exist, it will be created.

k6.RunContainer(ctx, WithCache(), k6.WithTestScript("/tests/test.js"))

WithCmdOptions

Use WithCmdOptions to pass a variadic list of strings as options to the k6 run command

k6.RunContainer(ctx, WithCmdOptions("--vus=10", "--duration=30s"), k6.WithTestScript("/tests/test.js"))

WithTestScript

Use the WithTestScript option to specify the test script to run. The path to the script must be an absolute path. This option copies the script file to the container and pass it to k6's run command. At least one WithTestScript or WithRemoteTestScript option must be specified.

k6.RunContainer(ctx, k6.WithTestScript("/tests/test.js"))

WithRemoteTestScript

Use the WithRemoteTestScript option to specify the remote test script to run. The path to the remote script must be a http or https url. Basic authentication is supported. This option performs a HTTP GET to copy the remote file locally then copies the script file to the container and pass it to k6's run command. The default timeout for the GET is 60 seconds. Only javascript, or more specifically Content-Type:text/javascript is supported. At least one WithTestScript or WithRemoteTestScript option must be specified.

scriptUrl:="https://raw.githubusercontent.com/testcontainers/testcontainers-go/main/modules/k6/scripts/pass.js"

uri, _ := url.Parse(scriptUrl)
desc := k6.DownloadableFile{Uri: *uri , DownloadDir: t.TempDir()}
options := k6.WithRemoteTestScript(desc)

k6.RunContainer(ctx, k6.WithCache(), options)

Container Methods

The K6 container does not expose any method.