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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 {
    panic(fmt.Errorf("failed to create httpbin container %w", err))
}

defer func() {
    if err := httpbin.Terminate(ctx); err != nil {
        panic(fmt.Errorf("failed to terminate container: %w", err))
    }
}()

httpbinIP, err := httpbin.ContainerIP(ctx)
if err != nil {
    panic(fmt.Errorf("failed to get httpbin IP: %w", err))
}

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 {
    panic(fmt.Errorf("failed to start k6 container: %w", err))
}

defer func() {
    if err := k6.Terminate(ctx); err != nil {
        panic(fmt.Errorf("failed to terminate container: %w", 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.

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 one single method: AsCommand(), which returns a slice of strings 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 started.

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.

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 option must be specified.

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

Container Methods

The K6 container does not expose any method.