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How do you fix 'Failed to load the dll hostfxr.dll' when starting an x86 .NET process in a test run via dotnet test?
How do you fix the error 'Failed to load the DLL hostfxr.dll' when running a .NET test executed via dotnet test and starting an x86 .NET application in the test?
I'm using .NET 8.
Failed to load the dll from [C:\Program Files\dotnet\host\fxr\8.0.4\hostfxr.dll], HRESULT: 0x800700C1
The library hostfxr.dll was found, but loading it from C:\Program Files\dotnet\host\fxr\8.0.4\hostfxr.dll failed
- Installing .NET prerequisites might help resolve this problem.
https://go.microsoft.com/fwlink/?linkid=798306
2 answers
The following users marked this post as Works for me:
| User | Comment | Date |
|---|---|---|
| riQQ | (no comment) | Oct 15, 2025 at 08:43 |
Remove
DOTNET_ROOTenvironment variable before process start
process.StartInfo.EnvironmentVariables.Remove("DOTNET_ROOT");
Another option is to use the x86 .NET SDK for running the tests:
& "C:\Program Files (x86)\dotnet\dotnet" test
Source: https://github.com/dotnet/sdk/issues/22647#issuecomment-973898754
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To fix this, you must ensure that the dotnet test runner executes as a 32-bit process to match the architecture of the application you are testing.
You have 2 solutions
-
Use the
--archFlag (Recommended for CI/CD)Run your test command with the
--arch x86flag:dotnet test --arch x86This flag forces the .NET host to use the 32-bit SDK and runtime (typically located in C:\Program Files (x86)\dotnet\), which can then correctly load and execute your x86 application.
-
Configure the Test Project (.csproj)
For a more permanent solution that works directly within Visual Studio or without needing a special command, you can configure your test project to always target the x86 platform.
Hope this helps!
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