Navigating the complex world of containerized testing environments can be challenging, especially when dealing with Docker-in-Docker (DinD). As a senior DevOps engineer and Docker Captain, I’ve seen firsthand the hurdles that teams face with DinD, and here I’ll share why Testcontainers Cloud is a transformative alternative that’s reshaping the way we handle container-based testing.

Understanding Docker-in-Docker

Docker-in-Docker allows you to run Docker within a Docker container. It’s like Inception for containers — a Docker daemon running inside a Docker container, capable of building and running other containers.

How Docker-in-Docker works

• Nested Docker daemons: In a typical Docker setup, the Docker daemon runs on the host machine, managing containers directly on the host’s operating system. With DinD, you start a Docker daemon inside a container. This inner Docker daemon operates independently, enabling the container to build and manage its own set of containers.
• Privileged mode and access to host resources: To run Docker inside a Docker container, the container needs elevated privileges. This is achieved by running the container in privileged mode using the --privileged flag:

docker run --privileged -d docker:dind

• The --privileged flag grants the container almost all the capabilities of the host machine, including access to device files and the ability to perform system administration tasks. Although this setup enables the inner Docker daemon to function, it poses significant security risks, as it can potentially allow the container to affect the host system adversely.

• Filesystem considerations: The inner Docker daemon stores images and containers within the file system of the DinD container, typically under /var/lib/docker. Because Docker uses advanced file system features like copy-on-write layers, running an inner Docker daemon within a containerized file system (which may itself use such features) can lead to complex interactions and potential conflicts.
• Cgroups and namespace isolation: Docker relies on Linux kernel features like cgroups and namespaces for resource isolation and management. When running Docker inside a container, these features must be correctly configured to allow nesting. This process can introduce additional complexity in ensuring that resource limits and isolation behave as expected.

Why teams use Docker-in-Docker

• Isolated build environments: DinD allows each continuous integration (CI) job to run in a clean, isolated Docker environment, ensuring that builds and tests are not affected by residual state from previous jobs or other jobs running concurrently.
• Consistency across environments: By encapsulating the Docker daemon within a container, teams can replicate the same Docker environment across different stages of the development pipeline, from local development to CI/CD systems.

Challenges with DinD

Although DinD provides certain benefits, it also introduces significant challenges, such as:

• Security risks: Running containers in privileged mode can expose the host system to security vulnerabilities, as the container gains extensive access to host resources.
• Stability issues: Nested containers can lead to storage driver conflicts and other instability issues, causing unpredictable build failures.
• Complex debugging: Troubleshooting issues in a nested Docker environment can be complicated, as it involves multiple layers of abstraction and isolation.

Real-world challenges

Although Docker-in-Docker might sound appealing, it often introduces more problems than it solves. Before diving into those challenges, let’s briefly discuss Testcontainers and its role in modern testing practices.

What is Testcontainers?

Testcontainers is a popular open source library designed to support integration testing by providing lightweight, disposable instances of common databases, web browsers, or any service that can run in a Docker container. It allows developers to write tests that interact with real instances of external resources, rather than relying on mocks or stubs.

Key features of Testcontainers

• Realistic testing environment: By using actual services in containers, tests are more reliable and closer to real-world scenarios.
• Isolation: Each test session, or even each test can run in a clean environment, reducing flakiness due to shared state.
• Easy cleanup: Containers are ephemeral and are automatically cleaned up after tests, preventing resource leaks.

Dependency on the Docker daemon

A core component of Testcontainers’ functionality lies in its interaction with the Docker daemon. Testcontainers orchestrates Docker resources by starting and stopping containers as needed for tests. This tight integration means that access to a Docker environment is essential wherever the tests are run.

The DinD challenge with Testcontainers in CI

When teams try to include Testcontainers-based integration testing in their CI/CD pipelines, they often face the challenge of providing Docker access within the CI environment. Because Testcontainers requires communication with the Docker daemon, many teams resort to using Docker-in-Docker to emulate a Docker environment inside the CI job.

However, this approach introduces significant challenges, especially when trying to scale Testcontainers usage across the organization.

Case study: The CI pipeline nightmare

We had a Jenkins CI pipeline that utilized Testcontainers for integration tests. To provide the necessary Docker environment, we implemented DinD. Initially, it seemed to work fine, but soon we encountered:

• Unstable builds: Random failures due to storage driver conflicts and issues with nested container layers. The nested Docker environment sometimes clashed with the host, causing unpredictable behavior.
• Security concerns: Running containers in privileged mode raised red flags during security audits. Because DinD requires privileged mode to function correctly, it posed significant security risks, potentially allowing containers to access the host system.
• Performance bottlenecks: Builds were slow, and resource consumption was high. The overhead of running Docker within Docker led to longer feedback loops, hindering developer productivity.
• Complex debugging: Troubleshooting nested containers became time-consuming. Logs and errors were difficult to trace through the multiple layers of containers, making issue resolution challenging.

We spent countless hours trying to patch these issues, but it felt like playing a game of whack-a-mole.

Why Testcontainers Cloud is a better choice

Testcontainers Cloud is a cloud-based service designed to simplify and enhance your container-based testing. By offloading container execution to the cloud, it provides a secure, scalable, and efficient environment for your integration tests.

How TestContainers Cloud addresses DinD’s shortcomings

Enhanced security

• No more privileged mode: Eliminates the need for running containers in privileged mode, reducing the attack surface.
• Isolation: Tests run in isolated cloud environments, minimizing risks to the host system.
• Compliance-friendly: Easier to pass security audits without exposing the Docker socket or granting elevated permissions.

Improved performance

• Scalability: Leverage cloud resources to run tests faster and handle higher loads.
• Resource efficiency: Offloading execution frees up local and CI/CD resources.

Simplified configuration

• Plug-and-play integration: Minimal changes are required to switch from local Docker to Testcontainers Cloud.
• No nested complexity: Avoid the intricacies and pitfalls of nested Docker daemons.

Better observability and debugging

• Detailed logs: Access comprehensive logs through the Testcontainers Cloud dashboard.
• Real-time monitoring: Monitor containers and resources in real time with enhanced visibility.

Getting started with Testcontainers Cloud

Let’s dive into how you can get the most out of Testcontainers Cloud.

Switching to Testcontainers Cloud allows you to run tests without needing a local Docker daemon:

• No local Docker required: Testcontainers Cloud handles container execution in the cloud.
• Consistent environment: Ensures that your tests run in the same environment across different machines.

Additionally, you can easily integrate Testcontainers Cloud into your CI pipeline to run the same tests without scaling your CI infrastructure.

Using Testcontainers Cloud with GitHub Actions

Here’s how you can set up Testcontainers Cloud in your GitHub Actions workflow.

1. Create a new service account

• Log in to Testcontainers Cloud dashboard.
• Navigate to Service Accounts:
  • Create a new service account dedicated to your CI environment.
• Generate an access token:
  • Copy the access token. Remember, you can only view it once, so store it securely.

2. Set the TC_CLOUD_TOKEN environment variable

• In GitHub Actions:
  • Go to your repository’s Settings > Secrets and variables > Actions.
  • Add a new Repository Secret named TC_CLOUD_TOKEN and paste the access token.

3. Add Testcontainers Cloud to your workflow

Update your GitHub Actions workflow (.github/workflows/ci.yml) to include the Testcontainers Cloud setup.

Example workflow:

name: CI Pipeline

on:
  push:
    branches: [ main ]
  pull_request:
    branches: [ main ]

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3

      # ... other preparation steps (dependencies, compilation, etc.) ...

      - name: Set up Java
        uses: actions/setup-java@v3
        with:
          distribution: 'temurin'
          java-version: '17'

      - name: Setup Testcontainers Cloud Client
        uses: atomicjar/testcontainers-cloud-setup-action@v1
        with:
          token: ${{ secrets.TC_CLOUD_TOKEN }}

      # ... steps to execute your tests ...
      - name: Run Tests
        run: ./mvnw test

Notes:

• The atomicjar/testcontainers-cloud-setup-action GitHub Action automates the installation and authentication of the Testcontainers Cloud Agent in your CI environment.
• Ensure that your TC_CLOUD_TOKEN is kept secure using GitHub’s encrypted secrets.

Clarifying the components: Testcontainers Cloud Agent and Testcontainers Cloud

To make everything clear:

• Testcontainers Cloud Agent (CLI in CI environments): In CI environments like GitHub Actions, you use the Testcontainers Cloud Agent (installed via the GitHub Action or command line) to connect your CI jobs to Testcontainers Cloud.
• Testcontainers Cloud: The cloud service that runs your containers, offloading execution from your CI environment.

In CI environments:

• Use the Testcontainers Cloud Agent (CLI) within your CI jobs.
• Authenticate using the TC_CLOUD_TOKEN.
• Tests executed in the CI environment will use Testcontainers Cloud.

Monitoring and debugging

Take advantage of the Testcontainers Cloud dashboard:

• Session logs: View logs for individual test sessions.
• Container details: Inspect container statuses and resource usage.
• Debugging: Access container logs and output for troubleshooting.

Why developers prefer Testcontainers Cloud over DinD

Real-world impact

After integrating Testcontainers Cloud, our team observed the following:

• Faster build times: Tests ran significantly faster due to optimized resource utilization.
• Reduced maintenance: Less time spent on debugging and fixing CI pipeline issues.
• Enhanced security: Eliminated the need for privileged mode, satisfying security audits.
• Better observability: Improved logging and monitoring capabilities.

Addressing common concerns

Security and compliance

• Data isolation: Each test runs in an isolated environment.
• Encrypted communication: Secure data transmission.
• Compliance: Meets industry-standard security practices.

Cost considerations

• Efficiency gains: Time saved on maintenance offsets the cost.
• Resource optimization: Reduces the need for expensive CI infrastructure.

Compatibility

• Multi-language support: Works with Java, Node.js, Python, Go, .NET, and more.
• Seamless integration: Minimal changes required to existing test code.

Conclusion

Switching to Testcontainers Cloud, with the help of the Testcontainers Cloud Agent, has been a game-changer for our team and many others in the industry. It addresses the key pain points associated with Docker-in-Docker and offers a secure, efficient, and developer-friendly alternative.

Key takeaways

• Security: Eliminates the need for privileged containers and Docker socket exposure.
• Performance: Accelerates test execution with scalable cloud resources.
• Simplicity: Simplifies configuration and reduces maintenance overhead.
• Observability: Enhances debugging with detailed logs and monitoring tools.

As someone who has navigated these challenges, I recommend trying Testcontainers Cloud. It’s time to move beyond the complexities of DinD and adopt a solution designed for modern development workflows.

Additional resources

• Testcontainers Cloud documentation:
  • Getting started
• Testcontainers library docs:
  • Java
  • Node.js
  • Python
• Best practices:
  • Testcontainers Best Practices
• Community support:
  • Join the Testcontainers Slack
  • GitHub discussions
  • Stack Overflow

When testing complex systems, the more edge cases you can identify, the better your software performs in the real world. But how do you efficiently generate hundreds or thousands of meaningful tests that reveal hidden bugs? Enter model-based testing (MBT), a technique that automates test case generation by modeling your software’s expected behavior.

In this demo, we’ll explore the model-based testing technique to perform regression testing on a simple REST API.

We’ll use the jqwik test engine on JUnit 5 to run property and model-based tests. Additionally, we’ll use Testcontainers to spin up Docker containers with different versions of our application.

Model-based testing

Model-based testing is a method for testing stateful software by comparing the tested component with a model that represents the expected behavior of the system. Instead of manually writing test cases, we’ll use a testing tool that:

• Takes a list of possible actions supported by the application
• Automatically generates test sequences from these actions, targeting potential edge cases
• Executes these tests on the software and the model, comparing the results

In our case, the actions are simply the endpoints exposed by the application’s API. For the demo’s code examples, we’ll use a basic service with a CRUD REST API that allows us to:

• Find an employee by their unique employee number
• Update an employee’s name
• Get a list of all the employees from a department
• Register a new employee

Once everything is configured and we finally run the test, we can expect to see a rapid sequence of hundreds of requests being sent to the two stateful services:

Docker Compose

Let’s assume we need to switch the database from Postgres to MySQL and want to ensure the service’s behavior remains consistent. To test this, we can run both versions of the application, send identical requests to each, and compare the responses.

We can set up the environment using a Docker Compose that will run two versions of the app:

• Model (mbt-demo:postgres): The current live version and our source of truth.
• Tested version (mbt-demo:mysql): The new feature branch under test.

services:
  ## MODEL
  app-model:
      image: mbt-demo:postgres
      # ...
      depends_on:
          - postgres
  postgres:
      image: postgres:16-alpine
      # ...
      
  ## TESTED
  app-tested:
    image: mbt-demo:mysql
    # ...
    depends_on:
      - mysql
  mysql:
    image: mysql:8.0
    # ...

Testcontainers

At this point, we could start the application and databases manually for testing, but this would be tedious. Instead, let’s use Testcontainers’ ComposeContainer to automate this with our Docker Compose file during the testing phase.

In this example, we’ll use jqwik as our JUnit 5 test runner. First, let’s add the jqwik and Testcontainers and the jqwik-testcontainers dependencies to our pom.xml:

<dependency>
    <groupId>net.jqwik</groupId>
    <artifactId>jqwik</artifactId>
    <version>1.9.0</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>net.jqwik</groupId>
    <artifactId>jqwik-testcontainers</artifactId>
    <version>0.5.2</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.testcontainers</groupId>
    <artifactId>testcontainers</artifactId>
    <version>1.20.1</version>
    <scope>test</scope>
</dependency>

As a result, we can now instantiate a ComposeContainer and pass our test docker-compose file as argument:

@Testcontainers
class ModelBasedTest {

    @Container
    static ComposeContainer ENV = new ComposeContainer(new File("src/test/resources/docker-compose-test.yml"))
       .withExposedService("app-tested", 8080, Wait.forHttp("/api/employees").forStatusCode(200))
       .withExposedService("app-model", 8080, Wait.forHttp("/api/employees").forStatusCode(200));

    // tests
}

Test HTTP client

Now, let’s create a small test utility that will help us execute the HTTP requests against our services:

class TestHttpClient {
  ApiResponse<EmployeeDto> get(String employeeNo) { /* ... */ }
  
  ApiResponse<Void> put(String employeeNo, String newName) { /* ... */ }
  
  ApiResponse<List<EmployeeDto>> getByDepartment(String department) { /* ... */ }
  
  ApiResponse<EmployeeDto> post(String employeeNo, String name) { /* ... */ }

    
  record ApiResponse<T>(int statusCode, @Nullable T body) { }
    
  record EmployeeDto(String employeeNo, String name) { }
}

Additionally, in the test class, we can declare another method that helps us create TestHttpClients for the two services started by the ComposeContainer:

static TestHttpClient testClient(String service) {
  int port = ENV.getServicePort(service, 8080);
  String url = "http://localhost:%s/api/employees".formatted(port);
  return new TestHttpClient(service, url);
}

jqwik

Jqwik is a property-based testing framework for Java that integrates with JUnit 5, automatically generating test cases to validate properties of code across diverse inputs. By using generators to create varied and random test inputs, jqwik enhances test coverage and uncovers edge cases.

If you’re new to jqwik, you can explore their API in detail by reviewing the official user guide. While this tutorial won’t cover all the specifics of the API, it’s essential to know that jqwik allows us to define a set of actions we want to test.

To begin with, we’ll use jqwik’s @Property annotation — instead of the traditional @Test — to define a test:

@Property
void regressionTest() {
  TestHttpClient model = testClient("app-model");
  TestHttpClient tested = testClient("app-tested");
  // ...
}

Next, we’ll define the actions, which are the HTTP calls to our APIs and can also include assertions.

For instance, the GetOneEmployeeAction will try to fetch a specific employee from both services and compare the responses:

record ModelVsTested(TestHttpClient model, TestHttpClient tested) {}

record GetOneEmployeeAction(String empNo) implements Action<ModelVsTested> {
  @Override
  public ModelVsTested run(ModelVsTested apps) {
    ApiResponse<EmployeeDto> actual = apps.tested.get(empNo);
    ApiResponse<EmployeeDto> expected = apps.model.get(empNo);

    assertThat(actual)
      .satisfies(hasStatusCode(expected.statusCode()))
      .satisfies(hasBody(expected.body()));
    return apps;
  }
}

Additionally, we’ll need to wrap these actions within Arbitrary objects. We can think of Arbitraries as objects implementing the factory design pattern that can generate a wide variety of instances of a type, based on a set of configured rules.

For instance, the Arbitrary returned by employeeNos() can generate employee numbers by choosing a random department from the configured list and concatenating a number between 0 and 200:

static Arbitrary<String> employeeNos() {
  Arbitrary<String> departments = Arbitraries.of("Frontend", "Backend", "HR", "Creative", "DevOps");
  Arbitrary<Long> ids = Arbitraries.longs().between(1, 200);
  return Combinators.combine(departments, ids).as("%s-%s"::formatted);
}

Similarly, getOneEmployeeAction() returns an Aribtrary action based on a given Arbitrary employee number:

static Arbitrary<GetOneEmployeeAction> getOneEmployeeAction() {
  return employeeNos().map(GetOneEmployeeAction::new);
}

After declaring all the other Actions and Arbitraries, we’ll create an ActionSequence:

@Provide
Arbitrary<ActionSequence<ModelVsTested>> mbtJqwikActions() {
  return Arbitraries.sequences(
    Arbitraries.oneOf(
      MbtJqwikActions.getOneEmployeeAction(),
      MbtJqwikActions.getEmployeesByDepartmentAction(),
      MbtJqwikActions.createEmployeeAction(),
      MbtJqwikActions.updateEmployeeNameAction()
  ));
}


static Arbitrary<Action<ModelVsTested>> getOneEmployeeAction() { /* ... */ }
static Arbitrary<Action<ModelVsTested>> getEmployeesByDepartmentAction() { /* ... */ }
// same for the other actions

Now, we can write our test and leverage jqwik to use the provided actions to test various sequences. Let’s create the ModelVsTested tuple and use it to execute the sequence of actions against it:

@Property
void regressionTest(@ForAll("mbtJqwikActions") ActionSequence<ModelVsTested> actions) {
  ModelVsTested testVsModel = new ModelVsTested(
    testClient("app-model"),
    testClient("app-tested")
  );
  actions.run(testVsModel);
}

That’s it — we can finally run the test! The test will generate a sequence of thousands of requests trying to find inconsistencies between the model and the tested service:

INFO com.etr.demo.utils.TestHttpClient -- [app-tested] PUT /api/employeesFrontend-129?name=v
INFO com.etr.demo.utils.TestHttpClient -- [app-model] PUT /api/employeesFrontend-129?name=v
INFO com.etr.demo.utils.TestHttpClient -- [app-tested] GET /api/employees/Frontend-129
INFO com.etr.demo.utils.TestHttpClient -- [app-model] GET /api/employees/Frontend-129
INFO com.etr.demo.utils.TestHttpClient -- [app-tested] POST /api/employees { name=sdxToS, empNo=Frontend-91 }
INFO com.etr.demo.utils.TestHttpClient -- [app-model] POST /api/employees { name=sdxToS, empNo=Frontend-91 }
INFO com.etr.demo.utils.TestHttpClient -- [app-tested] PUT /api/employeesFrontend-4?name=PZbmodNLNwX
INFO com.etr.demo.utils.TestHttpClient -- [app-model] PUT /api/employeesFrontend-4?name=PZbmodNLNwX
INFO com.etr.demo.utils.TestHttpClient -- [app-tested] GET /api/employees/Frontend-4
INFO com.etr.demo.utils.TestHttpClient -- [app-model] GET /api/employees/Frontend-4
INFO com.etr.demo.utils.TestHttpClient -- [app-tested] GET /api/employees?department=ٺ⯟桸
INFO com.etr.demo.utils.TestHttpClient -- [app-model] GET /api/employees?department=ٺ⯟桸
        ...

Catching errors

If we run the test and check the logs, we’ll quickly spot a failure. It appears that when searching for employees by department with the argument ٺ⯟桸 the model produces an internal server error, while the test version returns 200 OK:

Original Sample
---------------
actions:
ActionSequence[FAILED]: 8 actions run [
    UpdateEmployeeAction[empNo=Creative-13, newName=uRhplM],
    CreateEmployeeAction[empNo=Backend-184, name=aGAYQ],
    UpdateEmployeeAction[empNo=Backend-3, newName=aWCxzg],
    UpdateEmployeeAction[empNo=Frontend-93, newName=SrJTVwMvpy],
    UpdateEmployeeAction[empNo=Frontend-129, newName=v],
    CreateEmployeeAction[empNo=Frontend-91, name=sdxToS],
    UpdateEmployeeAction[empNo=Frontend-4, newName=PZbmodNLNwX],
    GetEmployeesByDepartmentAction[department=ٺ⯟桸]
]
    final currentModel: ModelVsTested[model=com.etr.demo.utils.TestHttpClient@5dc0ff7d, tested=com.etr.demo.utils.TestHttpClient@64920dc2]
Multiple Failures (1 failure)
    -- failure 1 --
    expected: 200
    but was: 500

Upon investigation, we find that the issue arises from a native SQL query using Postgres-specific syntax to retrieve data. While this was a simple issue in our small application, model-based testing can help uncover unexpected behavior that may only surface after a specific sequence of repetitive steps pushes the system into a particular state.

Wrap up

In this post, we provided hands-on examples of how model-based testing works in practice. From defining models to generating test cases, we’ve seen a powerful approach to improving test coverage and reducing manual effort. Now that you’ve seen the potential of model-based testing to enhance software quality, it’s time to dive deeper and tailor it to your own projects.

Clone the repository to experiment further, customize the models, and integrate this methodology into your testing strategy. Start building more resilient software today!

Thank you to Emanuel Trandafir for contributing this post.

Learn more

• Clone the model-based testing practice repo.
• Subscribe to the Docker Newsletter. 
• Visit the Testcontainers website.
• Get started with Testcontainers Cloud by creating a free account.
• Have questions? The Docker community is here to help.
• New to Docker? Get started.

This post was contributed by Jesús Espino, Principal Engineer at Mattermost.

In the ever-evolving software development landscape, ensuring robust and reliable plugin integration is no small feat. For Mattermost, relying solely on mocks for plugin testing became a limitation, leading to brittle tests and overlooked integration issues. Enter Testcontainers, an open source tool that provides isolated Docker environments, making complex integration testing not only feasible but efficient. 

In this blog post, we dive into how Mattermost has embraced Testcontainers to overhaul its testing strategy, achieving greater automation, improved accuracy, and seamless plugin integration with minimal overhead.

The previous approach

In the past, Mattermost relied heavily on mocks to test plugins. While this approach had its merits, it also had significant drawbacks. The tests were brittle, meaning they would often break when changes were made to the codebase. This made the tests challenging to develop and maintain, as developers had to constantly update the mocks to reflect the changes in the code.

Furthermore, the use of mocks meant that the integration aspect of testing was largely overlooked. The tests did not account for how the different components of the system interacted with each other, which could lead to unforeseen issues in the production environment. 

The previous approach additionally did not allow for proper integration testing in an automated way. The lack of automation made the testing process time-consuming and prone to human error. These challenges necessitated a shift in Mattermost’s testing strategy, leading to the adoption of Testcontainers for complex integration testing.

Mattermost’s approach to integration testing

Testcontainers for Go

Mattermost uses Testcontainers for Go to create an isolated testing environment for our plugins. This testing environment includes the Mattermost server, the PostgreSQL server, and, in certain cases, an API mock server. The plugin is then installed on the Mattermost server, and through regular API calls or end-to-end testing frameworks like Playwright, we perform the required testing.

We have created a specialized Testcontainers module for the Mattermost server. This module uses PostgreSQL as a dependency, ensuring that the testing environment closely mirrors the production environment. Our module allows the developer to install and configure any plugin you want in the Mattermost server easily.

To improve the system’s isolation, the Mattermost module includes a container for the server and a container for the PostgreSQL database, which are connected through an internal Docker network.

Additionally, the Mattermost module exposes utility functionality that allows direct access to the database, to the Mattermost API through the Go client, and some utility functions that enable admins to create users, channels, teams, and change the configuration, among other things. This functionality is invaluable for performing complex operations during testing, including API calls, users/teams/channel creation, configuration changes, or even SQL query execution. 

This approach provides a powerful set of tools with which to set up our tests and prepare everything for verifying the behavior that we expect. Combined with the disposable nature of the test container instances, this makes the system easy to understand while remaining isolated.

This comprehensive approach to testing ensures that all aspects of the Mattermost server and its plugins are thoroughly tested, thereby increasing their reliability and functionality. But, let’s see a code example of the usage.

We can start setting up our Mattermost environment with a plugin like this:

pluginConfig := map[string]any{}
options := []mmcontainer.MattermostCustomizeRequestOption{
  mmcontainer.WithPlugin("sample.tar.gz", "sample", pluginConfig),
}
mattermost, err := mmcontainer.RunContainer(context.Background(), options...)
defer mattermost.Terminate(context.Background()

Once your Mattermost instance is initialized, you can create a test like this:

func TestSample(t *testing.T) {
    client, err mattermost.GetClient()
    require.NoError(t, err)
    reqURL := client.URL + "/plugins/sample/sample-endpoint"
    resp, err := client.DoAPIRequest(context.Background(), http.MethodGet, reqURL, "", "")
    require.NoError(t, err, "cannot fetch url %s", reqURL)
    defer resp.Body.Close()
    bodyBytes, err := io.ReadAll(resp.Body)
    require.NoError(t, err)
    require.Equal(t, 200, resp.StatusCode)
    assert.Contains(t, string(bodyBytes), "sample-response") 
}

Here, you can decide when you tear down your Mattermost instance and recreate it. Once per test? Once per a set of tests? It is up to you and depends strictly on your needs and the nature of your tests.

Testcontainers for Node.js

In addition to using Testcontainers for Go, Mattermost leverages Testcontainers for Node.js to set up our testing environment. In case you’re unfamiliar, Testcontainers for Node.js is a Node.js library that provides similar functionality to Testcontainers for Go. Using Testcontainers for Node.js, we can set up our environment in the same way we did with Testcontainers for Go. This allows us to write Playwright tests using JavaScript and run them in the isolated Mattermost environment created by Testcontainers, enabling us to perform integration testing that interacts directly with the plugin user interface. The code is available on GitHub.  

This approach provides the same advantages as Testcontainers for Go, and it allows us to use a more interface-based testing tool — like Playwright in this case. Let me show a bit of code with the Node.js and Playwright implementation:

We start and stop the containers for each test:

test.beforeAll(async () => { mattermost = await RunContainer() })
test.afterAll(async () => { await mattermost.stop(); })

Then we can use our Mattermost instance like any other server running to run our Playwright tests:

test.describe('sample slash command', () => {
  test('try to run a sample slash command', async ({ page }) => {
    const url = mattermost.url()
    await login(page, url, "regularuser", "regularuser")
    await expect(page.getByLabel('town square public channel')).toBeVisible();
    await page.getByTestId('post_textbox').fill("/sample run")
    await page.getByTestId('SendMessageButton').click();
    await expect(page.getByText('Sample command result', { exact: true })).toBeVisible();
    await logout(page)
  });  
});

With these two approaches, we can create integration tests covering the API and the interface without having to mock or use any other synthetic environment. Also, we can test things in absolute isolation because we consciously decide whether we want to reuse the Testcontainers instances. We can also reach a high degree of isolation and thereby avoid the flakiness induced by contaminated environments when doing end-to-end testing.

Examples of usage

Currently, we are using this approach for two plugins.

1. Mattermost AI Copilot

This integration helps users in their daily tasks using AI large language models (LLMs), providing things like thread and meeting summarization and context-based interrogation.

This plugin has a rich interface, so we used the Testcontainers for Node and Playwright approach to ensure we could properly test the system through the interface. Also, this plugin needs to call the AI LLM through an API. To avoid that resource-heavy task, we use an API mock, another container that simulates any API.

This approach gives us confidence in the server-side code but in the interface side as well, because we can ensure that we aren’t breaking anything during the development.

2. Mattermost MS Teams plugin

This integration is designed to connect MS Teams and Mattermost in a seamless way, synchronizing messages between both platforms.

For this plugin, we mainly need to do API calls, so we used Testcontainers for Go and directly hit the API using a client written in Go. In this case, again, our plugin depends on a third-party service: the Microsoft Graph API from Microsoft. For that, we also use an API mock, enabling us to test the whole plugin without depending on the third-party service.

We still have some integration tests with the real Teams API using the same Testcontainers infrastructure to ensure that we are properly handling the Microsoft Graph calls.

Benefits of using Testcontainers libraries

Using Testcontainers for integration testing offers benefits, such as:

• Isolation: Each test runs in its own Docker container, which means that tests are completely isolated from each other. This approach prevents tests from interfering with one another and ensures that each test starts with a clean slate.
• Repeatability: Because the testing environment is set up automatically, the tests are highly repeatable. This means that developers can run the tests multiple times and get the same results, which increases the reliability of the tests.
• Ease of use: Testcontainers is easy to use, as it handles all the complexities of setting up and tearing down Docker containers. This allows developers to focus on writing tests rather than managing the testing environment.
  

Testing made easy with Testcontainers

Mattermost’s use of Testcontainers libraries for complex integration testing in their plugins is a testament to the power and versatility of Testcontainers.

By creating a well-isolated and repeatable testing environment, Mattermost ensures that our plugins are thoroughly tested and highly reliable.

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