Skip to content

How to create a container

Testcontainers are a wrapper around the Docker daemon designed for tests. Anything you can run in Docker, you can spin up with Testcontainers and integrate into your tests:

  • NoSQL databases or other data stores (e.g. Redis, ElasticSearch, MongoDB)
  • Web servers/proxies (e.g. NGINX, Apache)
  • Log services (e.g. Logstash, Kibana)
  • Other services developed by your team/organization which are already dockerized

Run

testcontainers.Run defines the container that should be run, similar to the docker run command.

func Run(ctx context.Context, img string, opts ...testcontainers.ContainerCustomizer) (*DockerContainer, error)
  • context.Context, the Go context.
  • string, the Docker image to use.
  • testcontainers.ContainerCustomizer, a variadic argument for passing options.

The following test creates an NGINX container on both the bridge (docker default network) and the foo network and validates that it returns 200 for the status code.

It also demonstrates how to use CleanupContainer, that ensures that nginx container is removed when the test ends even if the underlying container errored, as well as the CleanupNetwork which does the same for networks.

The alternatives for these outside of tests as a defer are TerminateContainer and Network.Remove which can be seen in the examples.

ctx := context.Background()

nw, err := network.New(ctx)
if err != nil {
    log.Printf("failed to create network: %s", err)
    return
}
defer func() {
    if err := nw.Remove(ctx); err != nil {
        log.Printf("failed to remove network: %s", err)
    }
}()

testFileContent := "Hello from file!"

ctr, err := testcontainers.Run(
    ctx,
    "nginx:alpine",
    network.WithNetwork([]string{"nginx-alias"}, nw),
    testcontainers.WithFiles(testcontainers.ContainerFile{
        Reader:            strings.NewReader(testFileContent),
        ContainerFilePath: "/tmp/file.txt",
        FileMode:          0o644,
    }),
    testcontainers.WithTmpfs(map[string]string{
        "/tmp": "rw",
    }),
    testcontainers.WithLabels(map[string]string{
        "testcontainers.label": "true",
    }),
    testcontainers.WithEnv(map[string]string{
        "TEST": "true",
    }),
    testcontainers.WithExposedPorts("80/tcp"),
    testcontainers.WithAfterReadyCommand(testcontainers.NewRawCommand([]string{"echo", "hello", "world"})),
    testcontainers.WithWaitStrategy(wait.ForListeningPort("80/tcp").WithStartupTimeout(time.Second*5)),
)
defer func() {
    if err := testcontainers.TerminateContainer(ctr); err != nil {
        log.Printf("failed to terminate container: %s", err)
    }
}()
if err != nil {
    log.Printf("failed to start container: %s", err)
    return
}

state, err := ctr.State(ctx)
if err != nil {
    log.Printf("failed to get container state: %s", err)
    return
}
fmt.Println(state.Running)

cli, err := testcontainers.NewDockerClientWithOpts(ctx)
if err != nil {
    log.Printf("failed to create docker client: %s", err)
    return
}

ctrResp, err := cli.ContainerInspect(ctx, ctr.GetContainerID())
if err != nil {
    log.Printf("failed to inspect container: %s", err)
    return
}

// networks
respNw, ok := ctrResp.NetworkSettings.Networks[nw.Name]
if !ok {
    log.Printf("network not found")
    return
}
fmt.Println(respNw.Aliases)

// env
fmt.Println(ctrResp.Config.Env[0])

// tmpfs
tmpfs, ok := ctrResp.HostConfig.Tmpfs["/tmp"]
if !ok {
    log.Printf("tmpfs not found")
    return
}
fmt.Println(tmpfs)

// labels
fmt.Println(ctrResp.Config.Labels["testcontainers.label"])

// files
// copyFileFromContainer {
f, err := ctr.CopyFileFromContainer(context.Background(), "/tmp/file.txt")
if err != nil {
    log.Printf("failed to copy file from container: %s", err)
    return
}

content, err := io.ReadAll(f)
if err != nil {
    log.Printf("failed to read file: %s", err)
    return
}
// }
fmt.Println(string(content))

// Output:
// true
// [nginx-alias]
// TEST=true
// rw
// true
// Hello from file!

Customizing the container

Basic Options

WithExposedPorts

If you need to expose additional ports from the container, you can use testcontainers.WithExposedPorts. For example:

ctr, err := mymodule.Run(ctx, "docker.io/myservice:1.2.3", 
    testcontainers.WithExposedPorts("8080/tcp", "9090/tcp"))
WithEnv

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

ctr, err = mymodule.Run(ctx, "docker.io/myservice:1.2.3", testcontainers.WithEnv(map[string]string{"FOO": "BAR"}))
WithWaitStrategy

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.

WithWaitStrategyAndDeadline

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

WithAdditionalWaitStrategy

If you need to add a wait strategy to the existing wait strategy, you can use testcontainers.WithAdditionalWaitStrategy.

Info

The default deadline for the wait strategy is 60 seconds.

WithAdditionalWaitStrategyAndDeadline

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

WithEntrypoint

If you need to completely replace the container's entrypoint, you can use testcontainers.WithEntrypoint. For example:

ctr, err := mymodule.Run(ctx, "docker.io/myservice:1.2.3", 
    testcontainers.WithEntrypoint("/bin/sh", "-c", "echo hello"))
WithEntrypointArgs

If you need to append commands to the container's entrypoint, you can use testcontainers.WithEntrypointArgs. For example:

ctr, err := mymodule.Run(ctx, "docker.io/myservice:1.2.3", 
    testcontainers.WithEntrypointArgs("echo", "hello"))
WithCmd

If you need to completely replace the container's command, you can use testcontainers.WithCmd. For example:

ctr, err := mymodule.Run(ctx, "docker.io/myservice:1.2.3", 
    testcontainers.WithCmd("echo", "hello"))
WithCmdArgs

If you need to append commands to the container's command, you can use testcontainers.WithCmdArgs. For example:

ctr, err := mymodule.Run(ctx, "docker.io/myservice:1.2.3", 
    testcontainers.WithCmdArgs("echo", "hello"))
WithLabels

If you need to add Docker labels to the container, you can use testcontainers.WithLabels. For example:

ctr, err := mymodule.Run(ctx, "docker.io/myservice:1.2.3", 
    testcontainers.WithLabels(map[string]string{
        "environment": "testing",
        "project":     "myapp",
    }))

Lifecycle Options

WithLifecycleHooks

If you need to set the lifecycle hooks for the container, you can use testcontainers.WithLifecycleHooks, which replaces the existing lifecycle hooks with the new ones.

WithAdditionalLifecycleHooks

You can also use testcontainers.WithAdditionalLifecycleHooks, which appends the new lifecycle hooks to the existing ones.

WithStartupCommand

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.

WithAfterReadyCommand

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.

Files & Mounts Options

WithFiles

If you need to copy files into the container, you can use testcontainers.WithFiles. For example:

ctr, err := mymodule.Run(ctx, "docker.io/myservice:1.2.3", 
    testcontainers.WithFiles([]testcontainers.ContainerFile{
        {
            HostFilePath:      "/path/to/local/file.txt",
            ContainerFilePath: "/container/file.txt",
            FileMode:          0o644,
        },
    }))

This option allows you to copy files from the host into the container at creation time.

WithMounts

If you need to add volume mounts to the container, you can use testcontainers.WithMounts. For example:

ctr, err := mymodule.Run(ctx, "docker.io/myservice:1.2.3", 
    testcontainers.WithMounts([]testcontainers.ContainerMount{
        {
            Source: testcontainers.GenericVolumeMountSource{Name: "appdata"},
            Target: "/app/data",
        },
    }))
WithTmpfs

If you need to add tmpfs mounts to the container, you can use testcontainers.WithTmpfs. For example:

ctr, err := mymodule.Run(ctx, "docker.io/myservice:1.2.3", 
    testcontainers.WithTmpfs(map[string]string{
        "/tmp": "size=100m",
        "/run": "size=100m",
    }))
WithImageMount

Since Docker v28, it's possible to mount an image to a container, passing the source image name, the relative subpath to mount in that image, and the mount point in the target container.

This option validates that the subpath is a relative path, raising an error otherwise.

newOllamaContainer, err := tcollama.Run(
    ctx,
    "ollama/ollama:0.5.12",
    testcontainers.WithImageMount(targetImage, "root/.ollama/models/", "/root/.ollama/models/"),
)

In the code above, which mounts the directory in which Ollama models are stored, the targetImage is the name of the image containing the models (an Ollama image where the models are already pulled).

Warning

Using this option fails the creation of the container if the underlying container runtime does not support the image mount feature.

Build Options

WithDockerfile

Testcontainers exposes the testcontainers.WithDockerfile option to build a container from a Dockerfile. The functional option receives a testcontainers.FromDockerfile struct that is applied to the container request before starting the container. As a result, the container is built and started in one go.

df := testcontainers.FromDockerfile{
    Context:    ".",
    Dockerfile: "Dockerfile",
    Repo:       "testcontainers",
    Tag:        "latest",
    BuildArgs:  map[string]*string{"ARG1": nil, "ARG2": nil},
}   

ctr, err := mymodule.Run(ctx, "docker.io/myservice:1.2.3", testcontainers.WithDockerfile(df))

Logging Options

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))
}
WithLogConsumerConfig

If you need to set the log consumer config for the container, you can use testcontainers.WithLogConsumerConfig. This option completely replaces the existing log consumer config, including the log consumers and the log production options.

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 the testcontainers-go log.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 := log.TestLogger(t)
    ctr, err := mymodule.Run(ctx, "docker.io/myservice:1.2.3", testcontainers.WithLogger(logger))
    CleanupContainer(t, ctr)
    require.NoError(t, err)
    // Do something with container.
}

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

Image Options

WithAlwaysPull

If you need to pull the image before starting the container, you can use testcontainers.WithAlwaysPull().

WithImageSubstitutors

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 operation: 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.

WithImagePlatform

If you need to set the platform for a container, you can use testcontainers.WithImagePlatform(platform string).

Networking Options

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.

WithNetworkByName

If you want to attach your containers to an already existing Docker network by its name, you can use the network.WithNetworkName(aliases []string, networkName string) option, which receives an alias as parameter and the network name, attaching the container to it, and setting the network alias for that network.

Warning

In case the network name is bridge, no aliases are set. This is because network-scoped alias is supported only for containers in user defined networks.

WithBridgeNetwork

If you want to attach your containers to the bridge network, you can use the network.WithBridgeNetwork() option.

Warning

The bridge network is the default network for Docker. It's not a user defined network, so it doesn't support network-scoped aliases.

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.

Advanced Options

WithHostPortAccess

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

ctr, err = mymodule.Run(ctx, "docker.io/myservice:1.2.3", testcontainers.WithHostPortAccess(8080))

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

WithConfigModifier

If you need an advanced configuration for the container, modifying the container's configuration, you can use the testcontainers.WithConfigModifier option, which gives access to the underlying Docker's Config type.

WithHostConfigModifier

If you need an advanced configuration for the container, modifying the container's host configuration, you can use the testcontainers.WithHostConfigModifier option, which gives access to the underlying Docker's HostConfig type.

WithEndpointSettingsModifier

If you need an advanced configuration for the container, modifying the container's endpoint settings, you can use the testcontainers.WithEndpointSettingsModifier option, which gives access to the underlying Docker's EndpointSettings type.

CustomizeRequest

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

ctr, err := mymodule.Run(ctx, "docker.io/myservice:1.2.3",
    /* 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.

WithName

If you need to set the name of the container, you can use the testcontainers.WithName option.

ctr, err := mymodule.Run(ctx, "docker.io/myservice:1.2.3", 
    testcontainers.WithName("my-container-name"),
)

Warning

This option is not checking whether the container name is already in use. If you use a name that is already in use, an error is returned. At the same time, we discourage using this option as it might lead to unexpected behavior, but we understand that in some cases it might be useful.

WithNoStart

If you need to prevent the container from being started after creation, you can use the testcontainers.WithNoStart option.

Experimental Options

WithReuseByName

This option marks a container to be reused if it exists or create a new one if it doesn't. With the current implementation, the container name must be provided to identify the container to be reused.

ctr, err := mymodule.Run(ctx, "docker.io/myservice:1.2.3", 
    testcontainers.WithReuseByName("my-container-name"),
)

Warning

Reusing a container is experimental and the API is subject to change for a more robust implementation that is not based on container names.

GenericContainer

Warning

GenericContainer is the old way to create a container, and we recommend using Run instead, as it could be deprecated in the future.

testcontainers.GenericContainer defines the container that should be run, similar to the docker run command.

The following test creates an NGINX container on both the bridge (docker default network) and the foo network and validates that it returns 200 for the status code.

It also demonstrates how to use CleanupContainer ensures that nginx container is removed when the test ends even if the underlying GenericContainer errored as well as the CleanupNetwork which does the same for networks.

The alternatives for these outside of tests as a defer are TerminateContainer and Network.Remove which can be seen in the examples.

package main

import (
    "context"
    "fmt"
    "net/http"
    "testing"

    "github.com/testcontainers/testcontainers-go"
    "github.com/testcontainers/testcontainers-go/wait"
)

type nginxContainer struct {
    testcontainers.Container
    URI string
}


func setupNginx(ctx context.Context, networkName string) (*nginxContainer, error) {
    req := testcontainers.ContainerRequest{
        Image:        "nginx",
        ExposedPorts: []string{"80/tcp"},
        Networks:     []string{"bridge", networkName},
        WaitingFor:   wait.ForHTTP("/"),
    }
    container, err := testcontainers.GenericContainer(ctx, testcontainers.GenericContainerRequest{
        ContainerRequest: req,
        Started:          true,
    })
    var nginxC *nginxContainer
    if container != nil {
        nginxC = &nginxContainer{Container: container}
    }
    if err != nil {
        return nginxC, err
    }

    ip, err := container.Host(ctx)
    if err != nil {
        return nginxC, err
    }

    mappedPort, err := container.MappedPort(ctx, "80")
    if err != nil {
        return nginxC, err
    }

    nginxC.URI = fmt.Sprintf("http://%s:%s", ip, mappedPort.Port())

    return nginxC, nil
}

func TestIntegrationNginxLatestReturn(t *testing.T) {
    if testing.Short() {
        t.Skip("skipping integration test")
    }

    ctx := context.Background()

    nw, err := network.New(ctx)
    require.NoError(t, err)
    testcontainers.CleanupNetwork(t, nw)

    nginxC, err := setupNginx(ctx, nw.Name)
    testcontainers.CleanupContainer(t, nginxC)
    require.NoError(t, err)

    resp, err := http.Get(nginxC.URI)
    require.Equal(t, http.StatusOK, resp.StatusCode)
}

Lifecycle hooks

Testcontainers for Go allows you to define your own lifecycle hooks for better control over your containers. You just need to define functions that return an error and receive the Go context as first argument, and a ContainerRequest for the Creating hook, and a Container for the rest of them as second argument.

You'll be able to pass multiple lifecycle hooks at the ContainerRequest as an array of testcontainers.ContainerLifecycleHooks. The testcontainers.ContainerLifecycleHooks struct defines the following lifecycle hooks, each of them backed by an array of functions representing the hooks:

  • PreBuilds - hooks that are executed before the image is built. This hook is only available when creating a container from a Dockerfile
  • PostBuilds - hooks that are executed after the image is built. This hook is only available when creating a container from a Dockerfile
  • PreCreates - hooks that are executed before the container is created
  • PostCreates - hooks that are executed after the container is created
  • PreStarts - hooks that are executed before the container is started
  • PostStarts - hooks that are executed after the container is started
  • PostReadies - hooks that are executed after the container is ready
  • PreStops - hooks that are executed before the container is stopped
  • PostStops - hooks that are executed after the container is stopped
  • PreTerminates - hooks that are executed before the container is terminated
  • PostTerminates - hooks that are executed after the container is terminated

Testcontainers for Go defines some default lifecycle hooks that are always executed in a specific order with respect to the user-defined hooks. The order of execution is the following:

  1. default pre hooks.
  2. user-defined pre hooks.
  3. user-defined post hooks.
  4. default post hooks.

Inside each group, the hooks will be executed in the order they were defined.

Info

The default hooks are for logging (applied to all hooks), customising the Docker config (applied to the pre-create hook), copying files in to the container (applied to the post-create hook), adding log consumers (applied to the post-start and pre-terminate hooks), and running the wait strategies as a readiness check (applied to the post-start hook).

It's important to notice that the Readiness of a container is defined by the wait strategies defined for the container. This hook will be executed right after the PostStarts hook. If you want to add your own readiness checks, you can do it by adding a PostReadies hook to the container request, which will execute your own readiness check after the default ones. That said, the PostStarts hooks don't warrant that the container is ready, so you should not rely on that.

Warning

Up to v0.37.0, the readiness hook included checks for all the exposed ports to be ready. This is not the case anymore, and the readiness hook only uses the wait strategies defined for the container to determine if the container is ready.

In the following example, we are going to create a container using all the lifecycle hooks, all of them printing a message when any of the lifecycle hooks is called:

req := ContainerRequest{
    Image: nginxAlpineImage,
    LifecycleHooks: []ContainerLifecycleHooks{
        {
            PreCreates: []ContainerRequestHook{
                func(_ context.Context, _ ContainerRequest) error {
                    prints = append(prints, "pre-create hook 1")
                    return nil
                },
                func(_ context.Context, _ ContainerRequest) error {
                    prints = append(prints, "pre-create hook 2")
                    return nil
                },
            },
            PostCreates: []ContainerHook{
                func(_ context.Context, _ Container) error {
                    prints = append(prints, "post-create hook 1")
                    return nil
                },
                func(_ context.Context, _ Container) error {
                    prints = append(prints, "post-create hook 2")
                    return nil
                },
            },
            PreStarts: []ContainerHook{
                func(_ context.Context, _ Container) error {
                    prints = append(prints, "pre-start hook 1")
                    return nil
                },
                func(_ context.Context, _ Container) error {
                    prints = append(prints, "pre-start hook 2")
                    return nil
                },
            },
            PostStarts: []ContainerHook{
                func(_ context.Context, _ Container) error {
                    prints = append(prints, "post-start hook 1")
                    return nil
                },
                func(_ context.Context, _ Container) error {
                    prints = append(prints, "post-start hook 2")
                    return nil
                },
            },
            PostReadies: []ContainerHook{
                func(_ context.Context, _ Container) error {
                    prints = append(prints, "post-ready hook 1")
                    return nil
                },
                func(_ context.Context, _ Container) error {
                    prints = append(prints, "post-ready hook 2")
                    return nil
                },
            },
            PreStops: []ContainerHook{
                func(_ context.Context, _ Container) error {
                    prints = append(prints, "pre-stop hook 1")
                    return nil
                },
                func(_ context.Context, _ Container) error {
                    prints = append(prints, "pre-stop hook 2")
                    return nil
                },
            },
            PostStops: []ContainerHook{
                func(_ context.Context, _ Container) error {
                    prints = append(prints, "post-stop hook 1")
                    return nil
                },
                func(_ context.Context, _ Container) error {
                    prints = append(prints, "post-stop hook 2")
                    return nil
                },
            },
            PreTerminates: []ContainerHook{
                func(_ context.Context, _ Container) error {
                    prints = append(prints, "pre-terminate hook 1")
                    return nil
                },
                func(_ context.Context, _ Container) error {
                    prints = append(prints, "pre-terminate hook 2")
                    return nil
                },
            },
            PostTerminates: []ContainerHook{
                func(_ context.Context, _ Container) error {
                    prints = append(prints, "post-terminate hook 1")
                    return nil
                },
                func(_ context.Context, _ Container) error {
                    prints = append(prints, "post-terminate hook 2")
                    return nil
                },
            },
        },
    },
}

Default Logging Hook

Testcontainers for Go comes with a default logging hook that will print a log message for each container lifecycle event, using the default logger. You can add your own logger by passing the testcontainers.DefaultLoggingHook option to the ContainerRequest, passing a reference to your preferred logger:

dl := inMemoryLogger{}

req := ContainerRequest{
    Image: nginxAlpineImage,
    LifecycleHooks: []ContainerLifecycleHooks{
        DefaultLoggingHook(&dl),
    },
}

type inMemoryLogger struct {
    data []string
}

func (l *inMemoryLogger) Printf(format string, args ...any) {
    l.data = append(l.data, fmt.Sprintf(format, args...))
}

Advanced Settings

The aforementioned GenericContainer function and the ContainerRequest struct represent a straightforward manner to configure the containers, but you could need to create your containers with more advance settings regarding the config, host config and endpoint settings Docker types. For those more advance settings, Testcontainers for Go offers a way to fully customize the container request and those internal Docker types. These customisations, called modifiers, will be applied just before the internal call to the Docker client to create the container.

req := ContainerRequest{
    Image: nginxAlpineImage, // alpine image does expose port 80
    ConfigModifier: func(config *container.Config) {
        config.Env = []string{"a=b"}
    },
    Mounts: ContainerMounts{
        {
            Source: DockerVolumeMountSource{
                Name: "appdata",
                VolumeOptions: &mount.VolumeOptions{
                    Labels: GenericLabels(),
                },
            },
            Target: "/data",
        },
    },
    HostConfigModifier: func(hostConfig *container.HostConfig) {
        hostConfig.PortBindings = nat.PortMap{
            "80/tcp": []nat.PortBinding{
                {
                    HostIP:   "1",
                    HostPort: "2",
                },
            },
        }
    },
    EndpointSettingsModifier: func(endpointSettings map[string]*network.EndpointSettings) {
        endpointSettings["a"] = &network.EndpointSettings{
            Aliases: []string{"b"},
            Links:   []string{"link1", "link2"},
        }
    },
}

Warning

The only special case where the modifiers are not applied last, is when there are no exposed ports in the container request and the container does not use a network mode from a container (e.g. req.NetworkMode = container.NetworkMode("container:$CONTAINER_ID")). In that case, Testcontainers for Go will extract the ports from the underlying Docker image and export them.

Reusable container

With Reuse option you can reuse an existing container. Reusing will work only if you pass an existing container name via 'req.Name' field. If the name is not in a list of existing containers, the function will create a new generic container. If Reuse is true and Name is empty, you will get error.

The following test creates an NGINX container, adds a file into it and then reuses the container again for checking the file: 

package main

import (
    "context"
    "fmt"
    "log"

    "github.com/testcontainers/testcontainers-go"
    "github.com/testcontainers/testcontainers-go/wait"
)

const (
    reusableContainerName = "my_test_reusable_container"
)

func main() {
    ctx := context.Background()

    n1, err := testcontainers.GenericContainer(ctx, testcontainers.GenericContainerRequest{
        ContainerRequest: testcontainers.ContainerRequest{
            Image:        "nginx:1.17.6",
            ExposedPorts: []string{"80/tcp"},
            WaitingFor:   wait.ForListeningPort("80/tcp"),
            Name:         reusableContainerName,
        },
        Started: true,
    })
    defer func() {
        if err := testcontainers.TerminateContainer(n1); err != nil {
            log.Printf("failed to terminate container: %s", err)
        }
    }()
    if err != nil {
        log.Print(err)
        return
    }

    copiedFileName := "hello_copy.sh"
    err = n1.CopyFileToContainer(ctx, "./testdata/hello.sh", "/"+copiedFileName, 700)

    if err != nil {
        log.Print(err)
        return
    }

    n2, err := testcontainers.GenericContainer(ctx, testcontainers.GenericContainerRequest{
        ContainerRequest: testcontainers.ContainerRequest{
            Image:        "nginx:1.17.6",
            ExposedPorts: []string{"80/tcp"},
            WaitingFor:   wait.ForListeningPort("80/tcp"),
            Name:         reusableContainerName,
        },
        Started: true,
        Reuse:   true,
    })
    defer func() {
        if err := testcontainers.TerminateContainer(n2); err != nil {
            log.Printf("failed to terminate container: %s", err)
        }
    }()
    if err != nil {
        log.Print(err)
        return
    }

    c, _, err := n2.Exec(ctx, []string{"bash", copiedFileName})
    if err != nil {
        log.Print(err)
        return
    }
    fmt.Println(c)
}

Parallel running

testcontainers.ParallelContainers - defines the containers that should be run in parallel mode.

The following test creates two NGINX containers in parallel:

package main

import (
    "context"
    "fmt"
    "log"

    "github.com/testcontainers/testcontainers-go"
)

func main() {
    ctx := context.Background()

    requests := testcontainers.ParallelContainerRequest{
        {
            ContainerRequest: testcontainers.ContainerRequest{

                Image: "nginx",
                ExposedPorts: []string{
                    "10080/tcp",
                },
            },
            Started: true,
        },
        {
            ContainerRequest: testcontainers.ContainerRequest{

                Image: "nginx",
                ExposedPorts: []string{
                    "10081/tcp",
                },
            },
            Started: true,
        },
    }

    res, err := testcontainers.ParallelContainers(ctx, requests, testcontainers.ParallelContainersOptions{})
    for _, c := range res {
        c := c
        defer func() {
            if err := testcontainers.TerminateContainer(c); err != nil {
                log.Printf("failed to terminate container: %s", c)
            }
        }()
    }

    if err != nil {
        e, ok := err.(testcontainers.ParallelContainersError)
        if !ok {
            log.Printf("unknown error: %v", err)
            return
        }

        for _, pe := range e.Errors {
            fmt.Println(pe.Request, pe.Error)
        }
        return
    }
}