Stryker.NET 4.8.1 fails to analyze .NET 9 projects - "Analyzing 0 projects"

[Vivihung]

Stryker.NET 4.8.1 fails to analyze .NET 9 projects - "Analyzing 0 projects"

Description

Stryker.NET 4.8.1 fails to find any projects to mutate when running against a .NET 9 test project, despite the test project having valid project references. The error message "No project references found. Please add a project reference to your test project and retry" is misleading, as project references exist and work correctly with dotnet build and dotnet test.

Environment

• Stryker.NET Version: 4.8.1
• .NET SDK Version: 9.0.307
• OS: Windows
• Target Framework: net9.0 (defined in Directory.Build.props)

Project Structure

src/
├── MyFeature/
│   ├── Service/
│   │   └── MyApp.MyFeature.Service.csproj
│   ├── Tests/
│   │   ├── MyApp.MyFeature.Tests.csproj (test project)
│   │   └── stryker-config.json
│   └── Shared/
│       └── MyApp.MyFeature.Shared.csproj
└── TestInfrastructure/
    ├── Infrastructure/
    │   └── MyApp.TestInfrastructure.csproj (marked with <IsTestProject>true</IsTestProject>)
    ├── Integration/
    │   └── MyApp.TestIntegration.csproj (marked with <IsTestProject>true</IsTestProject>)
    └── Shared/
        └── MyApp.TestShared.csproj (marked with <IsTestProject>true</IsTestProject>)

Test Project References

The test project (MyApp.MyFeature.Tests.csproj) contains:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <IsTestProject>true</IsTestProject>
  </PropertyGroup>

  <ItemGroup>
    <ProjectReference Include="..\Service\MyApp.MyFeature.Service.csproj" />
    <ProjectReference Include="..\..\TestInfrastructure\Infrastructure\MyApp.TestInfrastructure.csproj" />
    <ProjectReference Include="..\..\TestInfrastructure\Integration\MyApp.TestIntegration.csproj" />
    <ProjectReference Include="..\..\TestInfrastructure\Shared\MyApp.TestShared.csproj" />
  </ItemGroup>
</Project>

Stryker Configuration

stryker-config.json:

{
  "stryker-config": {
    "project": "MyApp.MyFeature.Service.csproj",
    "test-case-filter": "Category=Unit",
    "reporters": ["progress", "html", "cleartext"],
    "thresholds": { "high": 80, "low": 60, "break": 40 },
    "concurrency": 4,
    "mutation-level": "standard",
    "ignore-mutations": ["string"]
  }
}

Steps to Reproduce

1. Create a .NET 9 project with Directory.Build.props setting <TargetFramework>net9.0</TargetFramework>
2. Create a test project that references multiple projects (including test infrastructure projects)
3. Mark test infrastructure projects with <IsTestProject>true</IsTestProject>
4. Run dotnet stryker from the test project directory

Expected Behavior

Stryker should:

1. Identify the test project
2. Find the project references (especially MyApp.MyFeature.Service.csproj)
3. Begin mutation testing on the Service project

Actual Behavior

Stryker fails with:

[17:44:55 INF] Analyzing 1 test project(s).
[17:44:55 DBG] Analyzing 0 projects.
[17:44:55 DBG] Analyzing MyApp.MyFeature.Tests.csproj
[17:44:56 DBG] Analysis of project MyApp.MyFeature.Tests.csproj succeeded.

Stryker.NET failed to mutate your project. For more information see the logs below:

No project references found. Please add a project reference to your test project and retry.

The critical line is [17:44:55 DBG] Analyzing 0 projects. - Stryker is not detecting any projects to mutate.

Verification

The project builds and tests successfully:

$ cd src/MyFeature/Tests
$ dotnet build
# Build succeeded

$ dotnet test
# All tests pass

$ dotnet list reference
Project reference(s)
--------------------
..\Service\MyApp.MyFeature.Service.csproj
..\..\TestInfrastructure\Infrastructure\MyApp.TestInfrastructure.csproj
..\..\TestInfrastructure\Integration\MyApp.TestIntegration.csproj
..\..\TestInfrastructure\Shared\MyApp.TestShared.csproj

What I've Tried

1. ✅ Added "project": "MyApp.MyFeature.Service.csproj" to stryker-config.json
2. ✅ Passed --project "MyApp.MyFeature.Service.csproj" via command line
3. ✅ Marked all test infrastructure projects with <IsTestProject>true</IsTestProject>
4. ✅ Ran from both test project directory and service project directory (using --test-project)
5. ✅ Verified no Microsoft.NET.Test.Sdk package in the service project
6. ✅ Ran dotnet restore to ensure all references are resolved
7. ✅ Verified project builds successfully

None of these resolved the issue.

Hypothesis

This appears to be a .NET 9 compatibility issue. Stryker.NET 4.8.1's package description states it "requires the dotnet 8 runtime or newer" and targets net8.0, but may not properly support .NET 9 projects yet.

Full Debug Output

Click to expand full trace output

[17:44:55 INF] Logging enabled at level Trace
Version: 4.8.1
[17:44:55 DBG] Stryker starting, version: 4.8.1

[17:44:55 INF] Stryker will use a max of 4 parallel testsessions.
[17:44:55 DBG] Stryker started with options: {"MsBuildPath": null, "DevMode": false, "ProjectPath": "C:\\repo\\src\\MyFeature\\Tests", "IsSolutionContext": false, "WorkingDirectory": "C:\\repo\\src\\MyFeature\\Tests", "OutputPath": "C:\\repo\\src\\MyFeature\\Tests\\StrykerOutput\\2025-12-02.17-44-55", "ReportPath": "C:\\repo\\src\\MyFeature\\Tests\\StrykerOutput\\2025-12-02.17-44-55\\reports", "ReportFileName": "mutation-report", "SolutionPath": null, "Configuration": null, "TargetFramework": null, "LogOptions": {"LogToFile": false, "LogLevel": "Verbose", "$type": "LogOptions"}, "MutationLevel": "Standard", "Thresholds": {"High": 80, "Low": 60, "Break": 40, "$type": "Thresholds"}, "AdditionalTimeout": 5000, "LanguageVersion": "Default", "Concurrency": 4, "SourceProjectName": "MyApp.MyFeature.Service.csproj", "TestProjects": [], "TestCaseFilter": "Category=Unit", "Reporters": ["Progress", "Html", "ClearText"], "WithBaseline": false, "BaselineProvider": "Disk", "AzureFileStorageUrl": "", "AzureFileStorageSas": "", "DashboardUrl": "https://dashboard.stryker-mutator.io", "DashboardApiKey": null, "Since": false, "SinceTarget": "master", "DiffIgnoreChanges": [], "FallbackVersion": "master", "ModuleName": "", "ReportTypeToOpen": null, "Mutate": [{"Glob": {"Tokens": [{"TrailingPathSeparator": {"Value": "\\", "$type": "PathSeparatorToken"}, "LeadingPathSeparator": null, "$type": "WildcardDirectoryToken"}, {"$type": "WildcardToken"}], "$type": "Glob"}, "IsExclude": false, "TextSpans": [{"Start": 0, "End": 2147483647, "Length": 2147483647, "IsEmpty": false, "$type": "TextSpan"}], "$type": "FilePattern"}], "IgnoredMethods": [], "ExcludedMutations": ["String"], "ExcludedLinqExpressions": [], "OptimizationMode": "CoverageBasedTest", "ProjectName": "", "ProjectVersion": "", "BreakOnInitialTestFailure": false, "MutantIdProvider": {"$type": "BasicIdProvider"}, "$type": "StrykerOptions"}
[17:44:55 INF] Analysis starting.
[17:44:55 VRB] Scanned the directory C:\repo\src\MyFeature\Tests for *.csproj files: found ["C:\\repo\\src\\MyFeature\\Tests\\MyApp.MyFeature.Tests.csproj"]
[17:44:55 VRB] Found project file C:\repo\src\MyFeature\Tests\MyApp.MyFeature.Tests.csproj in path C:\repo\src\MyFeature\Tests
[17:44:55 DBG] Using C:\repo\src\MyFeature\Tests\MyApp.MyFeature.Tests.csproj as test project
[17:44:55 INF] Analyzing 1 test project(s).
[17:44:55 DBG] Analyzing 0 projects.
[17:44:55 DBG] Analyzing MyApp.MyFeature.Tests.csproj
[17:44:56 DBG] Analysis of project MyApp.MyFeature.Tests.csproj succeeded.
[17:44:56 INF] Analysis complete.
[17:44:56 INF] Time Elapsed 00:00:00.9518740

Stryker.NET failed to mutate your project. For more information see the logs below:

No project references found. Please add a project reference to your test project and retry.

[dupdob]

it looks like it should work. The best way for us to move forward on this is if you could share the project.
Here are a few checks you could try:

1. Remove the project option. Stryker should complain there are several candidate projects if everything works as expected. you can then reuse the project name it provides you for the project option and see if it solves your issue
2. Use solution mode: run Stryker from the solution folder without any project option. It should mutate all projects. If it fails, it should provide you with more information about the failure
3. try adding the --dev--mode option to the command line, it will provide supplemental information regarding why it fails

[bosquig]

It happened to me some time ago, I did the exact same thing that my colleagues did (and it worked for them) but it was failing with the same error message than you for some reason...

I formatted my windows and then it just worked.