Logic App Unit Test Framework Fails to Start – System.Runtime.InteropServices.OSPlatform Load Error Since 2025-05-08

[Veera-Pipuri]

I've been using the Logic App Unit Test Framework reliably for an extended period on my local machine without issues. However, starting on 2025-05-08, it suddenly began failing to start locally. I haven't made any changes to the framework code or my setup, so this appears to be an unexpected regression

below are the error details :

Error building configuration in an external startup class. Microsoft.Azure.Workflows.WebJobs.Extensions: Could not load type 'System.Runtime.InteropServices.OSPlatform' from assembly 'System.Runtime, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'.

A host error has occurred during startup operation Microsoft.Azure.WebJobs.Script: Error building configuration in an external startup class. Microsoft.Azure.Workflows.WebJobs.Extensions: Could not load type 'System.Runtime.InteropServices.OSPlatform' from assembly 'System.Runtime, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'.

Host startup operation has been canceled. LogicAppUnit.TestException: Functions runtime did not start properly. Please make sure you have the latest Azure Functions Core Tools installed and available on your PATH environment variable, and that Azurite is running.

[mark-abrams]

Hi @Veera-Pipuri , I don't believe that this is related to the unit testing framework - it relates to an issue with the Logic App extension in VS Code: https://learn.microsoft.com/en-us/answers/questions/2264356/logic-app-standard-workflow-fails-to-open-in-visua

Is your Logic App development environment working correctly?

[Veera-Pipuri]

Hi @mark-abrams,

While running test cases using the unit test framework, I started getting above error all of sudden. I suspect that a recent update to one of the NuGet packages may have affected the Azure Functions runtime startup.

Previously, the following configuration worked perfectly:

host. json

"extensionBundle": {
  "id": "Microsoft.Azure.Functions.ExtensionBundle",
  "version": "[4.*, 5.0.0)"
}

And in local.settings.json:

"FUNCTIONS_WORKER_RUNTIME": "dotnet"

This setup ran fine since the begining, and the tests executed successfully. However, all of a sudden, the function runtime started failing, and tests would not run.

To troubleshoot, I changed the configuration to:

host.json

"extensionBundle": {
  "id": "Microsoft.Azure.Functions.ExtensionBundle.Workflows",
  "version": "[1.*, 2.0.0)"
}

And updated the runtime to:

"FUNCTIONS_WORKER_RUNTIME": "node"

I also manually downloaded the Microsoft.Azure.Functions.ExtensionBundle.Workflows to: C:\Users\test.azure-functions-core-tools\Functions\ExtensionBundles\Microsoft.Azure.Functions.ExtensionBundle.Workflows\1.19.21

After these changes, the function runtime started successfully, and the test scripts executed without issues.

Do you think a recent update (e.g., NuGet packages, extension bundle, or Azure Functions Core Tools) could have caused the unit test framework to break?

[mark-abrams]

Yes, I believe that this is related to a recent update to Logic Apps. There are quite a few posts on the Internet about it.

Therefore I am going to close this issue.