`dotnet test` hangs when running integration tests with `UseWebpackDevMiddleware` in Azure DevOps

Description

Running the dotnet test task in Azure DevOps Pipelines on a test assembly that is running integration tests (via Microsoft.AspNetCore.Mvc.Testing) while also using UseWebpackDevMiddleware causes the test run to hang forever.

To Reproduce

1. Create a new ASP.NET Core SPA website (which uses UseWebpackDevMiddleware)
2. Create a unit test project that uses Microsoft.AspNetCore.Mvc.Testing to execute an integration test
3. Create an Azure DevOps Pipeline that builds and runs tests via dotnet build and dotnet test (I am using the Visual Studio 2019 on Windows 2019 build agent)
4. Run the pipeline and notice that when it gets to dotnet test, the test run hangs after logging the following:

Starting test execution, please wait...
info: Microsoft.AspNetCore.DataProtection.KeyManagement.XmlKeyManager[0]
      User profile is available. Using 'C:\Users\VssAdministrator\AppData\Local\ASP.NET\DataProtection-Keys' as key repository and Windows DPAPI to encrypt keys at rest.
info: Microsoft.AspNetCore.DataProtection.KeyManagement.XmlKeyManager[0]
      User profile is available. Using 'C:\Users\VssAdministrator\AppData\Local\ASP.NET\DataProtection-Keys' as key repository and Windows DPAPI to encrypt keys at rest.
info: Microsoft.AspNetCore.DataProtection.KeyManagement.XmlKeyManager[58]
      Creating key {5653a870-1f93-4b30-b7d2-29fd94a34191} with creation date 2019-05-23 17:34:18Z, activation date 2019-05-23 17:34:18Z, and expiration date 2019-08-21 17:34:18Z.
info: Microsoft.AspNetCore.DataProtection.KeyManagement.XmlKeyManager[58]
      Creating key {02253cc1-903b-43b6-909a-61faccc67c88} with creation date 2019-05-23 17:34:18Z, activation date 2019-05-23 17:34:18Z, and expiration date 2019-08-21 17:34:18Z.
info: Microsoft.AspNetCore.DataProtection.Repositories.FileSystemXmlRepository[39]
      Writing data to file 'C:\Users\VssAdministrator\AppData\Local\ASP.NET\DataProtection-Keys\key-5653a870-1f93-4b30-b7d2-29fd94a34191.xml'.
info: Microsoft.AspNetCore.DataProtection.Repositories.FileSystemXmlRepository[39]
      Writing data to file 'C:\Users\VssAdministrator\AppData\Local\ASP.NET\DataProtection-Keys\key-02253cc1-903b-43b6-909a-61faccc67c88.xml'.

Expected behavior

The test run should not hang due to the use of UseWebpackDevMiddleware.

Additional context

• I am using Azure DevOps Pipeline
• I am using version 2.2.300 of the dotnet SDK
• All of my packages are up to date (with no prerelease packages being used)
• The test run executes fine via Visual Studio and CLI locally
• I have tried using an agent hosted on a VM and the issue still occurs

[SidShetye]

Another issue is using code like

result = SomeAsyncMethodAsync(arg).Result;

in your test code. It basically comes from blocking in a multi-threaded scenario. Switching to the proper multi-threaded async/await pattern like

result = await SomeAsyncMethodAsync(arg);

gets things working again. Probably also why @axthosarouris 's work-around works, since it effectively disables multi-threading, masking this test code design problem.

Discovered this is older tests written back when async/await was new …

[ChristopherHaws]

We ended up switching to UseReactDevelopmentServer since UserWebpackDevMiddleware is being deprecated. The issue does not happen with UseReactDevelopmentServer. Thanks!