What is the intended purpose for the hierarchy provided in TestNode?

When reporting TestNode updates, you can include the parent test node UID. Looking at the code in Microsoft.Testing.Extensions.VSTestBridge for examples, it doesn't appear that any reporting there is using any hierarchy.

What do you envision the purpose of that hierarchy is, and how would it be reported to the user in Test Explorer? xUnit.net, for example, can make a case for its hierarchy being Assembly > Test Collection > Test Class > Test Method > Test Case > Test. Would it make sense for us to report all of that? Some of that? None of that?

Experimentation with dotnet test today shows that none of that appears to be used at the moment. Reporting parentless test results, just like the VSTestBridge, results in successful execution:

  $ .\src\xunit.v3.assert.tests\bin\Debug\net6.0\xunit.v3.assert.tests.exe

xUnit.net v3 In-Process Runner v0.1.1-pre.379-dev+f22e679603 (64-bit .NET 6.0.27)
  Discovering: xunit.v3.assert.tests (method display = ClassAndMethod, method display options = None)
  Discovered:  xunit.v3.assert.tests (1122 test cases to be run)
  Starting:    xunit.v3.assert.tests (parallel test collections = on [24 threads], stop on fail = off, explicit = off, seed = 1016941239, culture = invariant)
  Finished:    xunit.v3.assert.tests
=== TEST EXECUTION SUMMARY ===
   xunit.v3.assert.tests  Total: 1353, Errors: 0, Failed: 0, Skipped: 0, Not Run: 0, Time: 0.163s

  $ dotnet test src\xunit.v3.assert.tests --framework net6.0

  Determining projects to restore...
  All projects are up-to-date for restore.
  xunit.v3.assert -> C:\Dev\xunit\xunit\src\xunit.v3.assert\bin\Debug\net6.0\xunit.v3.assert.dll
  xunit.v3.common -> C:\Dev\xunit\xunit\src\xunit.v3.common\bin\Debug\netstandard2.0\xunit.v3.common.dll
  xunit.v3.core -> C:\Dev\xunit\xunit\src\xunit.v3.core\bin\Debug\netstandard2.0\xunit.v3.core.dll
  xunit.v3.runner.common -> C:\Dev\xunit\xunit\src\xunit.v3.runner.common\bin\Debug\netstandard2.0\xunit.v3.runner.common.dll
  xunit.v3.runner.inproc.console -> C:\Dev\xunit\xunit\src\xunit.v3.runner.inproc.console\bin\Debug\net6.0\xunit.v3.runner.inproc.console.dll
  xunit.v3.runner.utility -> C:\Dev\xunit\xunit\src\xunit.v3.runner.utility\bin\Debug\netstandard2.0\xunit.v3.runner.utility.netstandard20.dll
  xunit.v3.runner.tdnet -> C:\Dev\xunit\xunit\src\xunit.v3.runner.tdnet\bin\Debug\netstandard2.0\xunit.v3.runner.tdnet.dll
  xunit.v3.runner.tdnet -> C:\Dev\xunit\xunit\src\xunit.v3.runner.tdnet\bin\Debug\netstandard2.0\merged\xunit.v3.runner.tdnet.dll
  xunit.v3.assert.tests -> C:\Dev\xunit\xunit\src\xunit.v3.assert.tests\bin\Debug\net6.0\xunit.v3.assert.tests.dll
  Run tests: 'C:\Dev\xunit\xunit\src\xunit.v3.assert.tests\bin\Debug\net6.0\xunit.v3.assert.tests.dll' [net6.0|x64]
  Tests succeeded: 'C:\Dev\xunit\xunit\src\xunit.v3.assert.tests\bin\Debug\net6.0\xunit.v3.assert.tests.dll' [net6.0|x64]

  $ cat src\xunit.v3.assert.tests\bin\Debug\net6.0\TestResults\xunit.v3.assert.tests_net6.0_x64.log

Microsoft(R) Testing Platform Execution Command Line Tool
Version: 1.0.2+1686a9c93 (UTC 2024/02/21)
RuntimeInformation: win10-x64 - .NET 6.0.27
Copyright(c) Microsoft Corporation.  All rights reserved.
  Discovering: xunit.v3.assert.tests (method display = ClassAndMethod, method display options = None)
  Discovered:  xunit.v3.assert.tests (1122 test cases to be run)
  Starting:    xunit.v3.assert.tests (parallel test collections = on [24 threads], stop on fail = off, explicit = off, seed = 1016941239, culture = invariant)
  Finished:    xunit.v3.assert.tests
=== TEST EXECUTION SUMMARY ===
   xunit.v3.assert.tests  Total: 1353, Errors: 0, Failed: 0, Skipped: 0, Not Run: 0, Time: 0.158s
Passed! - Failed: 0, Passed: 1353, Skipped: 0, Total: 1353, Duration: 320ms - xunit.v3.assert.tests.dll (win10-x64 - .NET 6.0.27)

=== COMMAND LINE ===
C:\Program Files\dotnet\dotnet.exe exec C:\Dev\xunit\xunit\src\xunit.v3.assert.tests\bin\Debug\net6.0\xunit.v3.assert.tests.dll --internal-msbuild-node testingplatform.pipe.ae8e4422d11c4007b5802f10ca515653

I have not attempted to add any hierarchy (this is just experimental work at the moment), but I'm not sure how dotnet test would interpret that currently. Let's assume a single level of hierarchy (Assembly > Test) was supported. Would I report the assembly as "in progress", then at the end, report it as "failed" or "passed" based on whether any tests failed? How would that contribute to the test count in dotnet test? The API description of test node includes a node type of action vs. group (it would make sense that everything that's not a running test would be a group), but I don't see that reflected into the TestNode object in Microsoft.Testing.Platform. I'm presuming that every TestNode is implicitly an action node type right now; is that correct? So is it not possible to reporting groupings today?

Start with the linked TestNode protocol description and the Microsoft.Testing.Extensions.VSTestBridge reporting examples. Reproduce the parentless results with dotnet test, then investigate how action and group nodes, hierarchy, status, and test counts are currently interpreted. Done means a decided model for supported hierarchy and its reporting behavior, documented or implemented with corresponding tests.