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Document MTP generated code namespace conflicts in troubleshooting #54008

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Document MTP generated code namespace conflicts in troubleshooting
Evangelink May 25, 2026
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18 changes: 17 additions & 1 deletion docs/core/testing/microsoft-testing-platform-troubleshooting.md
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,7 @@ title: Microsoft.Testing.Platform (MTP) troubleshooting
description: Troubleshoot MTP issues, exit codes, and known problems.
author: Evangelink
ms.author: amauryleve
ms.date: 02/24/2026
ms.date: 05/25/2026
ai-usage: ai-assisted
---

Expand Down Expand Up @@ -86,6 +86,22 @@ Manually defining an entry point (`Main`) in a test project or referencing a tes

- Completely disable the transitive dependency to `Microsoft.Testing.Platform.MSBuild` by setting the `<IsTestingPlatformApplication>false</IsTestingPlatformApplication>` MSBuild property in the project that references a test project. This is needed when you reference a test project from a non-test project, for example, a console app that references a test application.

#### Generated code namespace conflicts with a referenced type

`Microsoft.Testing.Platform.MSBuild` generates the `SelfRegisteredExtensions` and `TestingPlatformEntryPoint` types inside the project's `$(RootNamespace)`. By default, `RootNamespace` matches the project name, which can collide with a type of the same fully qualified name exposed by a referenced assembly.

For example, a project named `System.Security.Cryptography.ProtectedData.Tests` ends up generating code in the `System.Security.Cryptography.ProtectedData` namespace. If the project also references the `System.Security.Cryptography.ProtectedData` NuGet package, which contains a public `ProtectedData` type under the `System.Security.Cryptography` namespace, the compiler can no longer disambiguate between the generated namespace and the referenced type, and emits errors such as `CS0118` ("'ProtectedData' is a namespace but is used like a type").

To resolve the conflict, override `RootNamespace` in your test project to a value that doesn't collide with any referenced type:

```xml
<PropertyGroup>
<RootNamespace>System.Security.Cryptography.ProtectedDataTests</RootNamespace>
</PropertyGroup>
```

You can also clear `RootNamespace` entirely (`<RootNamespace />`), in which case the generated types are emitted into the global namespace.

### Microsoft.Testing.Extensions.Fakes

#### Fakes error Failed to resolve profiler path from COR_PROFILER_PATH and COR_PROFILER environment variables
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