LambdaTestTool-v2 Debug Mode Fails For Rider

[mark-hopper]

Describe the feature

Current Limitation
The LambdaTestTool-v2 currently lacks the capability to support library based lambda projects (only supports standalone executable lambda projects).

In contrast, the original .NET Mock Lambda Test Tool included this feature, which we actively used in our workflow.

Use Case

Unable to test any library based lambda functions using the newer version of the tool, therefore using the first version without the new improvements mentioned.

Proposed Solution

Enhance LambdaTestTool-v2 by having the option to select the lambda function handler as you could previously in the first version. This will then enable us to migrate over to the newer version of the tool for our testing.

Other Information

No response

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

AWS .NET SDK and/or Package version used

N/A

Targeted .NET Platform

.NET 8

Operating System and version

OSX Tahoe

[GarrettBeatty]

https://github.com/aws/aws-lambda-dotnet/tree/master/Tools/LambdaTestTool-v2#option-2-using-class-library hi @mark-hopper . we support class library lambda functions. Wondering if your use case is the same as this or if its different can you share your setup/reproduction steps?

[mark-hopper]

https://github.com/aws/aws-lambda-dotnet/tree/master/Tools/LambdaTestTool-v2#option-2-using-class-library hi @mark-hopper . we support class library lambda functions. Wondering if your use case is the same as this or if its different can you share your setup/reproduction steps?

So, I have a standalone lambda function (no inputs or outputs) which we will eventually invoke on a schedule. So I just wanted to invoke that handler via the test tool rather than having to convert to a console, setup what I need in the console and run it manually. I think I discounted that option you mentioned as it looked like it was only suitable with testing via API Gateway emulation as well?

[ashishdhingra]

Needs review with the team. In new version of tool, Lambda project runs as a separate executable, and the tool acts as an API emulator, communicating via an environment variable AWS_LAMBDA_RUNTIME_API. In previous version of the tool, it loaded the compiled class library into its own process.

[GarrettBeatty]

https://github.com/GarrettBeatty/MyLambdaFunctiuon/tree/master/MyLambdaFunction @mark-hopper here is an example without api gateway. I am using a class library function. can you see if this is similar to what your setup would be?

the readme has steps to run it

[mark-hopper]

https://github.com/GarrettBeatty/MyLambdaFunctiuon/tree/master/MyLambdaFunction @mark-hopper here is an example without api gateway. I am using a class library function. can you see if this is similar to what your setup would be?

the readme has steps to run it

Thank you @GarrettBeatty I'll take a look when I can and get back to you

[GarrettBeatty]

also as a side note, if your project also happens to already use Aspire, we also have https://github.com/aws/integrations-on-dotnet-aspire-for-aws/tree/main/src/Aspire.Hosting.AWS#integrating-aws-lambda-local-development This takes care of a lot of the manual configuration with the test tool.

[mark-hopper]

@GarrettBeatty thanks for your sample project, it would appear we are only able to run the lambda project but not debug it, is that expected?

For context I am using Rider / macOS for my development environment. But running the project (as opposed to debugging does work), if I debug I get the following:

2026-01-12T16:35:31.743Z fail Amazon.Lambda.RuntimeSupport.ExceptionHandling.LambdaValidationException: Could not find the specified handler assembly with the file name 'MyLambdaFunction, Culture=neutral, PublicKeyToken=null'. The assembly should be located in the root of your uploaded .zip file. at Amazon.Lambda.RuntimeSupport.Bootstrap.UserCodeLoader.Init(Action1 customerLoggingAction) in C:\build\Libraries\src\Amazon.Lambda.RuntimeSupport\Bootstrap\UserCodeLoader.cs:line 100
at Amazon.Lambda.RuntimeSupport.Bootstrap.UserCodeInitializer.InitializeAsync() in C:\build\Libraries\src\Amazon.Lambda.RuntimeSupport\Bootstrap\UserCodeInitializer.cs:line 46
at Amazon.Lambda.RuntimeSupport.LambdaBootstrap.InitializeAsync() in C:\build\Libraries\src\Amazon.Lambda.RuntimeSupport\Bootstrap\LambdaBootstrap.cs:line 242
Unhandled exception. HTTP Response:

Amazon.Lambda.RuntimeSupport.RuntimeApiClientException: The HTTP status code of the response was not expected (400).

Status: 400
Response:

at Amazon.Lambda.RuntimeSupport.InternalRuntimeApiClient.ErrorAsync(String lambda_Runtime_Function_Error_Type, String errorJson, String url, CancellationToken cancellationToken) in C:\build\Libraries\src\Amazon.Lambda.RuntimeSupport\Client\InternalClientAdapted.cs:line 204
at Amazon.Lambda.RuntimeSupport.LambdaBootstrap.InitializeAsync() in C:\build\Libraries\src\Amazon.Lambda.RuntimeSupport\Bootstrap\LambdaBootstrap.cs:line 247
at Amazon.Lambda.RuntimeSupport.LambdaBootstrap.RunAsync(CancellationToken cancellationToken) in C:\build\Libraries\src\Amazon.Lambda.RuntimeSupport\Bootstrap\LambdaBootstrap.cs:line 188
at Amazon.Lambda.RuntimeSupport.RuntimeSupportInitializer.RunLambdaBootstrap() in C:\build\Libraries\src\Amazon.Lambda.RuntimeSupport\RuntimeSupportInitializer.cs:line 70
at Amazon.Lambda.RuntimeSupport.Program.Main(String[] args) in C:\build\Libraries\src\Amazon.Lambda.RuntimeSupport\Program.cs:line 48
at Amazon.Lambda.RuntimeSupport.Program.

(String[] args)
`

[GarrettBeatty]

I will try to test on mac today. i was testing on windows with visual studio just now

i will try out rider with my mac

[GarrettBeatty]

I was able to reproduce your issue on my mac (fails in debug mode), but succeeds in regular run mode