Fixing 'Cannot start the driver service on http://localhost: ... already in use' when integrating E2E tests for Blazor with Selenium in Gitlab CI

Question

I am rather new to CI and I am trying to integrate selenium in gitlab ci for a dotnet blazor project with c#. The e2e tests with selenium are working on my machine. I have to write them for firefox and chrome. I used Program.CreateHostBuilder(new string[0]).Build().RunAsync(); to start the app on [SetUp] in nunit for e2e tests.

I am reading out different connectionString due to different enviroments with

 if (String.CompareOrdinal(Environment.MachineName, "runner") == 0)
            {
                return configuration.GetConnectionString("Pipeline");
            }
 return configuration.GetConnectionString("Local");

This is what my .gitlab-ci.yml currently looks like:

image: mcr.microsoft.com/dotnet/sdk:5.0

stages:
  - build
  - test


before_script:
    - "cd Project/Team01"
    - "dotnet restore"

build:
  tags:
    - pro
  stage: build
  script:
    - "dotnet build"

test:
  tags:
    - pro
  stage: test
  services:
  - name: mcmoe/mssqldocker:v2017.CU24.0
    alias: mssql
  - selenium/standalone-chrome
  - selenium/standalone-firefox

  variables:
    ACCEPT_EULA: Y
    SA_PASSWORD: SomeStrongPW
    MSSQL_DB: db
    MSSQL_USER: Dev
    MSSQL_PASSWORD: DatabasPW

  script:
    - "dotnet test"

When I run the pipeline all the e2e are failing with the following error message:

OpenQA.Selenium.WebDriverException : Cannot start the driver service on http://localhost:43471/
TearDown : System.NullReferenceException : Object reference not set to an instance of an object.
Stack Trace:
     at OpenQA.Selenium.DriverService.Start()
   at OpenQA.Selenium.Remote.DriverServiceCommandExecutor.Execute(Command commandToExecute)
   at OpenQA.Selenium.Remote.RemoteWebDriver.Execute(String driverCommandToExecute, Dictionary`2 parameters)
...

When I scroll down a little bit more I find the following:

Unable to start Kestrel.
       System.IO.IOException: Failed to bind to address http://127.0.0.1:5000: address already in use.
        ---> Microsoft.AspNetCore.Connections.AddressInUseException: Address already in use
        ---> System.Net.Sockets.SocketException (98): Address already in use
          at System.Net.Sockets.Socket.UpdateStatusAfterSocketErrorAndThrowException(SocketError error, String callerName)

When I look at the first error message I found here and here though not connected to CI sadly. It seems it might be an error with installing the correct webdriver or some other configuration not set up properly. I am also wondering why the address should be already in use since I can't see anything which is using it.

For setting up the configuration I mainly found this post useful, looked at this and this as reference.

• with the gitlab docs I can't understand how to use the wdio.conf.js and where to put it and how the confidence check would be connected to be used in my test stage.
• the documentation from one post above seems quite confusing since there is a lot configured and I cant make any sense what each line is required for.
  • the same goes for using cucumber since it is quite ruby connected and I also can't find any clue on how to use it for other browsers
• here I see that a lot of details went in there I don't understand and I am having a hard time how to use it for other drivers, though it seems to be the most straigt forward in my opinion.

I feel a little stuck since I see only half baken answers on really specific cases and I am not sure what would be best practice for blazor and c#, since most answers are referring to other programing languages.

Please let me know if you need any further details. Thanks in advance! Any hints or solutions are appreciated.

update 1

• I tried using npm though I realized I can't use to images at the same time
• defined the localhost to port 4444 on ap startup.

I still get the same errors though, I changed to

  - name: selenium/standalone-chrome:latest
  - name: selenium/standalone-firefox:latest

in my yml. I would like to know how I can pass different parameters regarding the port.

update 2

I tried to add the following to gitlab-ci.yml:

install:
  image: docker:stable
  script:
    - docker run -d -p 4444:4444 -v /dev/shm:/dev/shm selenium/standalone-firefox:4.0.0-beta-4-prerelease-20210527
    - docker run -d -p 4444:4444 -v /dev/shm:/dev/shm selenium/standalone-chrome:4.0.0-beta-4-prerelease-20210527
  artifacts:
    paths:
      - test

which I got from this documentation, also moved the image for dotnet to the other stages.