How to Run Dotnet Test Alongside Docker Compose in GitLab CI/CD

To run dotnet test in GitLab and have it connect to and use containerized services like databases, caches, or in this case Selenium Hub, you can use the following pattern:

1. Rely on GitLab CI’s built-in docker:dind (“docker in docker”) service to run docker commands as job scripts.
2. Install docker-compose manually (if you know of a way to somehow use an image instead for this, let me know!)
3. Run docker-compose using a test-specific docker-compose.yml.
4. Run dotnet test using docker run [...] mcr.microsoft.com/dotnet/sdk:5.0 dotnet test [...].

Example xUnit Test Class

This is using xUnit, pulling the Selenium Hub URL from appsettings.json, and grabbing the title of google.com.

SomeBrowserTests.cs

public class SomeBrowserTests
{
    [Fact]
    public void GetTitleTest()
    {
        var env = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT");
        var configuration = new ConfigurationBuilder()
            .AddJsonFile("appsettings.json")
            .AddJsonFile($"appsettings.{env}.json", optional: true)
            .Build();
        var webDriverHubUrl = configuration.GetSection("Selenium")["HubUrl"];
        var options = new ChromeOptions();
        var hubUri = new Uri(webDriverHubUrl);
        using var driver = new RemoteWebDriver(hubUri, options);

        driver.Url = "https://www.google.com";
        var title = driver.Title;

        Assert.Contains("Google", title);

        driver.Quit();
    }
}

Example appsettings.json

This is the appsettings.json that GitLab CI will use. For local development it’s possible to use a separate appsettings.json pointed to localhost, since a local docker-compose setup for development would expose the necessary ports on localhost. However, GitLab CI creates a new container for each job script, so anything running there will have to connect from the a test container to the Selenium Hub container using the container name that docker provides via it’s magic DNS stuff. (this took me a long time to figure out, and adding a job script of docker network ls helped.)

appsettings.CI.json

{
  "Selenium": {
    "HubUrl": "http://some-selenium-hub:4444/wd/hub"
  }
}

Example docker-compose.yml

Nothing fancy here (this is close to what the Selenium docs show), other than to note what network name (bridged by default) is used (some-tests) because it will be used later when running dotnet test.

docker-compose.some-tests.yml

version: "3.3"

networks:
  some-tests:

services:

  some-selenium-chrome:
    image: selenium/node-chrome:4.0
    restart: always
    volumes:
      - /dev/shm:/dev/shm
    environment:
      - SE_EVENT_BUS_HOST=some-selenium-hub
      - SE_EVENT_BUS_PUBLISH_PORT=4442
      - SE_EVENT_BUS_SUBSCRIBE_PORT=4443
    entrypoint: bash -c 'SE_OPTS="--host $$HOSTNAME" /opt/bin/entry_point.sh'
    networks:
      - some-tests
    depends_on:
      - some-selenium-hub

  some-selenium-hub:
    image: selenium/hub:4.0
    restart: always
    ports:
      - "4442:4442"
      - "4443:4443"
      - "4444:4444"
    networks:
      - some-tests

Example .gitlab-ci.yml

Here’s where the rubber meets the road.

• Alpine now allows apk add docker-compose (so there’s no need to mess with python/pip installation of docker-compose 🙌).
• After docker-compose is installed, start the Selenium Hub.
• Then run the dotnet tests:
  • Notice it runs the dotnet/sdk image in the same some-tests network (so that it can connect to http://some-selenium-hub:4444/wd/hub)
  • Notice it sets the ASPNETCORE_ENVIRONMENT=CI (so that the test will read from the appsettings.CI.json configuration)
  • Notice it mounts -v $PWD:/app so that the output from --logger "junit" will be readable by the GitLab CI task runner to capture test results. This requires the JUnitTestLogger nuget package to be installed in the test project(s).
  • Notice it calls docker-compose down, and I’m not entirely sure that’s necessary – I just like to be a good citizen.

.gitlab-ci.yml

image: docker:latest
services:
  - name: docker:dind
    entrypoint: ["dockerd-entrypoint.sh"]
    command: ["--max-concurrent-downloads", "6"]

stages:
  - test

variables:
  DOCKER_DRIVER: overlay2

some-tests:
  stage: test
  before_script:
    - apk add docker-compose
  script:
    - docker-compose -f docker-compose.some-tests.yml up -d --build --remove-orphans
    - docker run --network some-tests -v $PWD:/app -w /app -e "ASPNETCORE_ENVIRONMENT=CI" mcr.microsoft.com/dotnet/sdk:5.0-alpine dotnet test SomeSolution.sln --logger "junit"
    - docker-compose -f docker-compose.some-tests.yml down
  artifacts:
    reports:
      junit: ./**/TestResults/TestResults.xml