Exception while using Testcontainers to run tests in a container

[AndrewPearson]

Running tests using Testcontainers from within a container results in exceptions being thrown. The same tests pass when run locally (i.e. not in a container).

The following is a typical stack trace of the exceptions thrown:

System.TypeInitializationException : The type initializer for 'DotNet.Testcontainers.Configurations.TestcontainersSettings' threw an exception.
---- System.InvalidOperationException : Sequence contains no elements
  Stack Trace:
     at DotNet.Testcontainers.Configurations.TestcontainersSettings.get_OS()
...

Is additional config required to run Testcontainers within a container? Or is this a bug?

To Reproduce Steps to reproduce the behavior:

1. Set up an xUnit project containing a single test class, using the PostgreSqlTest test class shown on the main README for testcontainers-dotnet, using the following nuget packages:
   • Testcontainers 2.1.0
   • Npgsql 6.0,.6
   • xUnit 2.4.2
2. Add a Dockerfile to build and run the tests (using mcr.microsoft.com/dotnet/sdk:6.0).
3. Build & run the test project in a container.

Screenshots

[xUnit.net 00:00:00.71]     Tests.PostgreSqlTest.ExecuteCommand [FAIL]
  Failed Tests.PostgreSqlTest.ExecuteCommand [1 ms]
  Error Message:
   System.TypeInitializationException : The type initializer for 'DotNet.Testcontainers.Configurations.TestcontainersSettings' threw an exception.
---- System.InvalidOperationException : Sequence contains no elements
  Stack Trace:
     at DotNet.Testcontainers.Configurations.TestcontainersSettings.get_OS()
   at Tests.PostgreSqlTest..ctor() in /Tests/PostgreSqlTest.cs:line 15
   at System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean wrapExceptions)
----- Inner Stack Trace -----
   at System.Linq.ParallelEnumerable.GetOneWithPossibleDefault[TSource](QueryOperator`1 queryOp, Boolean throwIfTwo, Boolean defaultIfEmpty)
   at System.Linq.ParallelEnumerable.First[TSource](ParallelQuery`1 source)
   at DotNet.Testcontainers.Configurations.TestcontainersSettings..cctor()

Expected behavior The test should pass.

Desktop (please complete the following information):

• Running on Windows 10 (Build 19044.1865).
• Docker Desktop For Windows 4.11.0 (83626). Using linux containers & WSL2.
• .Net SDK 6.0.302

[HofmeisterAn]

Testcontainers cannot find the Docker endpoint, see: #528, #529, https://github.com/testcontainers/testcontainers-dotnet/discussions/543#discussioncomment-3299997. Add the env variable DOCKER_HOST e.g.

[AndrewPearson]

What should DOCKER_HOST be set to for Docker running locally? host.docker.internal doesn't resolve the problem.

[HofmeisterAn]

Is additional config required to run Testcontainers within a container? Or is this a bug?

This is not a bug. Docker is not running inside your container. Either use a different Docker host or use something like Docker in Docker (DinD).

What should DOCKER_HOST be set to for Docker running locally? host.docker.internal doesn't resolve the problem.

This can be any exposed Docker API endpoint. Maybe this helps to understand your issue too.

[AndrewPearson]

Thanks for taking the time to help. I'm afraid it's just not working with DinD. I'll have to find something else.

[HofmeisterAn]

I'm afraid it's just not working with DinD.

It is working. I am using it too. Here are some more information: https://github.com/testcontainers/testcontainers-dotnet/issues/492#issuecomment-1171283803.

[HofmeisterAn]

@AndrewPearson did the comment help? Do you need any further help or can we close this issue?

[AndrewPearson]

@HofmeisterAn Sorry for the slow reply, I've been offline for a couple of weeks. I'm afraid the previous comment was interesting but it didn't help. There are lots of suggestions in the various links, but they're all fragments of a working solution and there's nothing I have seen that I can really use to learn how this is done.

It's ok to close this issue.

[HofmeisterAn]

No worries. The linked comment contains everything to setup an example with Docker.

[AndrewPearson]

I worked it out finally. Thanks for your help.

[pdevito3]

I worked it out finally. Thanks for your help.

@AndrewPearson how did you end up resolving this? getting the same error after updating the lib for my local tests

[AndrewPearson]

@pdevito3 My initial requirement was to get this working in a container running locally on Docker Desktop for Windows. In the end all that was required was to map my local /var/run/docker.sock as a volume in the container.

On Windows, docker.sock is available as //var/run/docker.sock. This differs slightly from the path available on other OS's.

If you're using docker-compose then add a volume entry like the following to your service declaration:

    volumes:
      - //var/run/docker.sock:/var/run/docker.sock

If you're using docker run then map the same volumes with the -v option.

For me that was all that was required to get things working.