platform-detection

name	platform-detection
description	Identify a .NET project's test platform, framework, command mode, and SDK-style vs classic project system. Use only for "which test platform/framework?", "VSTest or MTP?", or "what runner does this project use?", including bridge settings, UseVSTest opt-outs, and incompatible or conflicting VSTest/MTP configuration. Resolves global.json, project, packages.config, Directory.Build.props, and Directory.Packages.props precedence for MSTest/xUnit/NUnit/TUnit. For running/filtering tests, exact commands or flags, TRX/dumps, and test-command/filter errors, use run-tests. Do not use for hot reload or migration.
license	MIT

Test Platform and Framework Detection

Determine which test platform (VSTest or Microsoft.Testing.Platform) and which test framework (MSTest, xUnit, NUnit, TUnit) a project uses.

Response contract

Honor the user's requested labels and order exactly, substituting the actual classification for every placeholder. Start with the verdict: never put a heading, scratch analysis, tool syntax, or an echoed template before it. Follow with one concise evidence sentence naming the repository facts needed to justify every requested classification. When Framework is requested, name the package or project SDK that identifies it. Use a second sentence only for a conflict, an incomplete configuration, or target-framework-specific differences.

Platform means the platform that actually executes tests: VSTest or MTP. If conflicting or incomplete configuration prevents execution, report it as unavailable rather than inventing a successful platform.

Apply this scope gate before drafting the evidence:

User asks for	Evidence to include	Omit
Platform and framework	Final runner selector and its winning source; package or project SDK identifying the framework; when needed, the property that makes it executable	Command mode; common SDK facts; OutputType unless it is missing or conflicting
The single deciding signal	That runner-selection property, why its source wins, and why a competing package does not select or imply VSTest; still name the package or project SDK identifying a requested framework	Bridge, OutputType, SDK mode, and unrelated prerequisites when the configuration is complete
Platforms per target framework	Only the conditional final values that differ by target	Common properties and project-wide SDK commentary
Explicit opt-out	Final UseVSTest value and its winning source	Superseded defaults unless they create a conflict
dotnet test mode	The separate command-mode and executed-platform classifications	None of the requested axes

If the requested labels omit dotnet test mode, do not state or explain command mode anywhere in the response. An exact bridge property may still be decisive platform evidence, but do not turn it into SDK or CLI-mode commentary.

When import precedence decides a property, state why the winning source wins (for example, it is imported later or its condition applies), not merely that it contains the final value or overrides another assignment.

Keep the explanation on the requested axis:

• An SDK version pin in global.json is context, not a platform selector. Claim that global.json selects VSTest or native MTP only when its test.runner setting actually does so.
• If UseVSTest=true is decisive, say that directly. Do not speculate about an absent test.runner or describe SDK pinning as an additional platform choice.
• If command mode was not requested, do not add it, even when it was needed internally to determine the executed platform.

When a classic-project request also asks for the command family, add a direct line such as Command family: MSBuild + vstest.console.exe; do not turn it into an optional alternative or add an unnecessary build qualifier.

For a file-backed request, enumerate the following configuration names once, then read every relevant file that is present in one batched operation: global.json, .csproj, packages.config, Directory.Build.props, Directory.Build.targets, Directory.Packages.props, and explicit imported .props / .targets. A setting absent from the project file may be defined by an import, so never infer its final value from the .csproj alone. Do not search the web or inspect unrelated files when repository configuration is sufficient.

Resolve properties in the actual MSBuild import order, not with a fixed "project beats props" rule. For every applicable target framework:

1. Follow the import graph and conditions. A later applicable assignment wins. Directory.Build.props is normally imported before the project body, so an unconditional project assignment normally overrides it; later .targets can override the project again.
2. Record the final value and its winning source for UseVSTest, the framework runner selector, TestingPlatformDotnetTestSupport, and OutputType.
3. Treat Directory.Packages.props as version evidence unless it also contains relevant properties. Resolve package/SDK versions before applying version-dependent defaults.
4. Never infer a property from package presence. A package or SDK default counts only when that resolved version actually supplies it and no later assignment overrides it.

Detecting the project system

Classify the project before selecting a CLI:

• Root Sdk attribute or <Sdk> declaration: SDK-style.
• ToolsVersion, Microsoft.Common.props / Microsoft.CSharp.targets imports, explicit <Reference> and <Compile Include> items: classic non-SDK.
• packages.config: classic NuGet dependency management.

Classic projects can still use VSTest-compatible adapters, but dotnet test is not automatically a valid invocation. Preserve repository scripts/CI commands, commonly MSBuild followed by vstest.console.exe. Mention MSTest.exe only when repository configuration or documentation establishes that legacy runner.

Detecting the test framework

Read the .csproj, adjacent packages.config, and Directory.Build.props / Directory.Packages.props and look for:

Package or SDK reference	Framework
MSTest metapackage, <Project Sdk="MSTest.Sdk[/version]">, or <Sdk Name="MSTest.Sdk">	MSTest
MSTest.TestFramework + MSTest.TestAdapter	MSTest (also valid for v3/v4)
xunit, xunit.v3, xunit.v3.mtp-v1, xunit.v3.mtp-v2, xunit.v3.core.mtp-v1, xunit.v3.core.mtp-v2	xUnit
NUnit + NUnit3TestAdapter	NUnit
TUnit	TUnit (MTP only)

In classic projects, package IDs and versions may appear only in packages.config, while the project contains assembly <Reference> elements with HintPath values. Use both sources.

Detecting the executed test platform

If the user explicitly requests dotnet test mode, read references/command-mode.md before answering. Do not load that reference or mention command mode for a platform/framework-only request.

For an SDK 8/9 request that explicitly asks about command mode and has no effective bridge, state all three facts in one causal sentence: the runner makes the project MTP-capable, dotnet test remains in VSTest mode, and the missing bridge means VSTest actually executes the tests. Mention that native MTP command mode starts with SDK 10 only when it helps explain that result.

When execution is permitted and neither the prompt nor global.json identifies the SDK, run dotnet --version once. For read-only identification requests that prohibit execution, do not probe the installed SDK; use repository facts and state any necessary SDK assumption.

After resolving final property values, classify in this order:

1. Final UseVSTest=true selects VSTest. If global.json simultaneously selects native MTP command mode, report Platform: unavailable because the command mode and project opt-out conflict.
2. A native-MTP selection in global.json executes a compatible MTP application with final OutputType=Exe on MTP. A VSTest-only, library-output, or opted-out project is unavailable.
3. On SDK 8/9, an enabled MTP runner plus final TestingPlatformDotnetTestSupport=true plus final OutputType=Exe executes on MTP.
4. If the runner is enabled but the bridge is absent or false, a dual-capable MSTest, NUnit, or xUnit project remains on VSTest: the runner establishes MTP capability, but SDK 8/9 dotnet test cannot reach it and the VSTest adapter executes the tests instead. If the bridge is true but no runner is enabled, the project also remains on VSTest.
5. A runner and bridge with non-executable output is incomplete and unavailable. An MTP-only framework that cannot be reached by the selected SDK path is also unavailable, not VSTest.

Keep each signal's role exact:

• The runner property selects the test application.
• TestingPlatformDotnetTestSupport=true lets SDK 8/9 dotnet test reach that application.
• OutputType=Exe supplies the executable host shape. It does not select or enable MTP.

Do not confuse the MSTest metapackage with the MSTest.Sdk project SDK. PackageReference Include="MSTest" plus EnableMSTestRunner=true enables the MSTest MTP runner, but it does not implicitly set TestingPlatformDotnetTestSupport.

MSTest.Sdk enables the MTP runner by default. Check its resolved version and evaluated properties for bridge behavior: version 3.8 supplies TestingPlatformDotnetTestSupport unless a later assignment overrides it, while newer SDKs on .NET 10 may expect native MTP mode instead. <UseVSTest>true</UseVSTest> opts back into VSTest.

Signal	Meaning
<Project Sdk="MSTest.Sdk..."> with no UseVSTest	MTP application; inspect the resolved SDK version and evaluated bridge property
MSTest metapackage + <EnableMSTestRunner>true>	MTP runner enabled; does not imply the VSTest-to-MTP bridge
<UseMicrosoftTestingPlatformRunner>true	Deciding xUnit runner-selection signal
<EnableMSTestRunner>true> / <EnableNUnitRunner>true>	Deciding MSTest/NUnit runner-selection signal
TestingPlatformDotnetTestSupport=true	Execution prerequisite for a VSTest-to-MTP bridge, not the runner-selection signal
Microsoft.Testing.Platform package	MTP-capable application; not decisive by itself
TUnit	MTP-only framework
Final evaluated <OutputType>Exe</OutputType>	Required executable host shape for package-based MTP applications

Microsoft.NET.Test.Sdk alone is not decisive; it can remain for compatibility in an MTP-enabled project. When an explicit override decides the result, name the final override and its source, not the superseded default. When a runner-selection property competes with Microsoft.NET.Test.Sdk, say that the runner property selects MTP and Microsoft.NET.Test.Sdk does not select or imply VSTest. It may remain as compatibility support, but that is secondary. TestingPlatformDotnetTestSupport=true is a bridge prerequisite, not the runner-selection signal; never say that this property alone enables the bridge. For a request asking which single signal decides, stop there. Omit bridge or host-shape prerequisites when the configuration is complete, and add them only when needed to explain why the selected runner cannot execute.

Use causal evidence, not a bag of signals. For example:

Platform: MTP
Framework: NUnit

Directory.Build.props supplies final EnableNUnitRunner=true and
TestingPlatformDotnetTestSupport=true, so NUnit executes on MTP.

For an incompatible configuration, give one minimal alignment choice after the verdict without modifying files: either select the project's configured platform globally or remove the project opt-out to use the globally selected platform.

Conditional and per-target-framework properties

Evaluate runner and bridge properties for each target framework. If conditions produce different executed platforms, report each target explicitly (for example, net8.0: VSTest, net9.0: MTP) rather than collapsing the project to one global platform.