Support `--config-file` flag for testconfig.json location (MTP)

[EraYaN]

Describe the bug
As a continuation on #1887 it would be awesome if coverlet could respect the same switch as the rest of the test configuration so we don't ave to copy it to the output directory. Currently coverlet ignores the config file if it does not live in the output directory.

To Reproduce

dotnet test --config-file testconfig.json --project .\subdir\projectName.csproj --diagnostic --diagnostic-verbosity Trace

with a project using coverlet.MTP. (and the correct global.json config to enable MTP)

{
  "platformOptions": {
    "Coverlet": {
      "Include": "[Calcasa.*]*",
      "Exclude": "[coverlet.*]*,[Microsoft.VisualStudio.TestPlatform.*]*,[testhost*]*,[coverlet.*.Tests?]*,[*]Coverlet.Core*,[*]Moq*,[*]TestBase*",
      "excludeByAttribute": "Obsolete,GeneratedCodeAttribute,CompilerGeneratedAttribute,ExcludeFromCodeCoverage,ExcludeFromCodeCoverageAttribute",
      "excludeByFile": "**/*Migrations/*.cs",
      "format": "cobertura,opencover",
      "useSourceLink": false,
      "singleHit": false,
      "includeTestAssembly": false,
      "skipAutoProps": true,
      "deterministicReport": false,
      "excludeAssembliesWithoutSources": "MissingAll"
    }
  }
}

Expected behavior
This should output the correct value in the diagnostic and respect the config items.

Actual behavior
It uses the default config.

Configuration (please complete the following information):
Please provide more information on your .NET configuration:
* Which coverlet package (collector, console, msbuild, ...) and version was used? coverlet.MTP 10.0.1
* Which version of .NET is the code running on? 10.0
* What OS and version, and what distro if applicable? Windows 11
* What is the architecture (x64, x86, ARM, ARM64)? x64
* Do you know whether it is specific to that configuration? Also fails on Ubuntu 26.04 x64

[Bertk]

Thank you for the information. Could you provide more details about your test project configuration?

I believe this issue is related to the coverlet.MTP documentation. Please remove CopyToOutputDirectory and try again.

The platform will automatically detect and load the [appname].testconfig.json file located in the output directory of the test project (close to the executable).

Source: https://learn.microsoft.com/en-us/dotnet/core/testing/microsoft-testing-platform-config

example test project:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFrameworks>$(NetMinimum);$(NetCurrent)</TargetFrameworks>
    <DebugType>portable</DebugType>
    <OutputType>Exe</OutputType>
    <IsPackable>false</IsPackable>
    <IsTestProject>true</IsTestProject>
    <TestingPlatformShowTestsFailure>true</TestingPlatformShowTestsFailure>
    <UseMicrosoftTestingPlatformRunner>true</UseMicrosoftTestingPlatformRunner>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="coverlet.MTP" />
    <PackageReference Include="xunit.v3.mtp-v2" />
    <PackageReference Include="Microsoft.Testing.Extensions.GitHubActionsReport" />
   </ItemGroup>

  <ItemGroup>
    <ProjectReference Include="..\..\src\ClassLibrary1\ClassLibrary1.csproj" />
  </ItemGroup>

  
</Project>

excerpt from coverlet.MTP diagnostic.log file

2026-08-20T07:26:52.9212511+00:00 Microsoft.Testing.Platform.Builder.TestApplication INFORMATION TESTINGPLATFORM_DEFAULT_HANG_TIMEOUT: ''
2026-08-20T07:26:52.9588324+00:00 Microsoft.Testing.Platform.Hosts.TestHostBuilder INFORMATION Setting RegisterEnvironmentVariablesConfigurationSource: 'True'
2026-08-20T07:26:52.9650489+00:00 Microsoft.Testing.Platform.Configurations.JsonConfigurationSource+JsonConfigurationProvider INFORMATION Config file 'C:\GitHub\coverlet-examples\artifacts\bin\XUnitProject1.Tests\debug_net10.0\XUnitProject1.Tests.testconfig.json' loaded.
2026-08-20T07:26:52.9778953+00:00 ConfigurationManager TRACE Configuration file ('C:\GitHub\coverlet-examples\artifacts\bin\XUnitProject1.Tests\debug_net10.0\XUnitProject1.Tests.testconfig.json') content:
{
  "platformOptions": {
    "Coverlet": {
      "Exclude": "[*.Tests]*,[xunit*]*",
      "ExcludeByAttribute": "GeneratedCode,ExcludeFromCodeCoverage",
      "Format": "cobertura,json,lcov,opencover",
      "SkipAutoProps": true,
      "ExcludeAssembliesWithoutSources": "MissingAll"
    }
  }
}

2026-08-20T07:26:52.9803045+00:00 Microsoft.Testing.Platform.Hosts.TestHostBuilder INFORMATION Setting PlatformExitProcessOnUnhandledException: 'False', config file: False environment variable: 
2026-08-20T07:26:53.0438542+00:00 Microsoft.Testing.Platform.Telemetry.TelemetryManager DEBUG TestApplicationOptions.EnableTelemetry: True
2026-08-20T07:26:53.0439113+00:00 Microsoft.Testing.Platform.Telemetry.TelemetryManager DEBUG TESTINGPLATFORM_TELEMETRY_OPTOUT environment variable: '1'
2026-08-20T07:26:53.0439134+00:00 Microsoft.Testing.Platform.Telemetry.TelemetryManager DEBUG DOTNET_CLI_TELEMETRY_OPTOUT environment variable: '1'
2026-08-20T07:26:53.0439141+00:00 Microsoft.Testing.Platform.Telemetry.TelemetryManager DEBUG Telemetry is 'DISABLED'
2026-08-20T07:26:53.0630197+00:00 Coverlet TRACE [DIAG] CoverletExtensionCollector constructor - running in controller process
2026-08-20T07:26:53.0630508+00:00 Coverlet TRACE [DIAG]   Process ID: 9460
2026-08-20T07:26:53.0877104+00:00 Microsoft.Testing.Platform.Hosts.TestHostControllersTestHost DEBUG Test host controller process info: Process: C:\GitHub\coverlet-examples\artifacts\bin\XUnitProject1.Tests\debug_net10.0\XUnitProject1.Tests.exe, Arguments: --report-xunit-trx --results-directory ./artifacts/results --coverlet --coverlet-output-format cobertura --diagnostic --diagnostic-verbosity trace --diagnostic-file-prefix XUnitProject1 --report-gh, Workspace: C:\GitHub\coverlet-examples\artifacts\bin\XUnitProject1.Tests\debug_net10.0
2026-08-20T07:26:53.0886516+00:00 Microsoft.Testing.Platform.Hosts.TestHostControllersTestHost DEBUG TESTINGPLATFORM_TESTHOSTCONTROLLER_CORRELATIONID_9460 '9b2ec78ca6b64db690acdb259e476d93'
2026-08-20T07:26:53.1017934+00:00 coverlet.MTP.EnvironmentVariables.CoverletExtensionEnvironmentVariableProvider DEBUG [CoverletEnvVarProvider] Set COVERLET_MTP_COVERAGE_ENABLED=true
2026-08-20T07:26:53.1045884+00:00 Coverlet TRACE === BeforeTestHostProcessStartAsync START ===
2026-08-20T07:26:53.1046143+00:00 Coverlet TRACE Controller PID: 9460
2026-08-20T07:26:53.1046186+00:00 Coverlet TRACE Coverage enabled (--coverlet flag): True
2026-08-20T07:26:53.1054806+00:00 Coverlet TRACE Found testconfig.json: C:\GitHub\coverlet-examples\artifacts\bin\XUnitProject1.Tests\debug_net10.0\XUnitProject1.Tests.testconfig.json
2026-08-20T07:26:53.1171595+00:00 Coverlet TRACE testconfig.json settings loaded: Format=cobertura,json,lcov,opencover, IncludeTestAssembly=False
2026-08-20T07:26:53.1176066+00:00 CollectorExtension DEBUG [Default] coverlet-deterministic-report: False
2026-08-20T07:26:53.1179743+00:00 CollectorExtension DEBUG [config file] coverlet-does-not-return-attribute: (empty)
2026-08-20T07:26:53.1181790+00:00 CollectorExtension DEBUG [config file] coverlet-exclude-assemblies-without-sources: MissingAll
2026-08-20T07:26:53.1184087+00:00 CollectorExtension DEBUG [config file] coverlet-exclude-by-attribute: GeneratedCode, ExcludeFromCodeCoverage
2026-08-20T07:26:53.1186091+00:00 CollectorExtension DEBUG [config file] coverlet-exclude: [coverlet.*]*, [*.Tests]*, [xunit*]*
2026-08-20T07:26:53.1187864+00:00 CollectorExtension DEBUG [config file] coverlet-exclude-by-file: (empty)
2026-08-20T07:26:53.1189470+00:00 CollectorExtension DEBUG [config file] coverlet-include-directory: (empty)
2026-08-20T07:26:53.1191055+00:00 CollectorExtension DEBUG [config file] coverlet-include: (empty)
2026-08-20T07:26:53.1192054+00:00 CollectorExtension DEBUG [Default] coverlet-include-test-assembly: False
2026-08-20T07:26:53.1193644+00:00 CollectorExtension DEBUG [Default] coverlet-single-hit: False
2026-08-20T07:26:53.1194796+00:00 CollectorExtension DEBUG [Config file] coverlet-skip-auto-props: True
2026-08-20T07:26:53.1196257+00:00 CollectorExtension DEBUG [Explicitly set] coverlet-output-format: cobertura
2026-08-20T07:26:53.1198352+00:00 Coverlet TRACE Test module path: C:\GitHub\coverlet-examples\artifacts\bin\XUnitProject1.Tests\debug_net10.0\XUnitProject1.Tests.dll
2026-08-20T07:26:53.1325778+00:00 Coverlet TRACE Coverlet configuration: Coverlet.MTP.Configuration.CoverletExtensionConfiguration
2026-08-20T07:26:53.1497482+00:00 Coverlet INFORMATION [Important] _mapping file name: 'CoverletSourceRootsMapping_XUnitProject1.Tests'
2026-08-20T07:26:53.1542379+00:00 Coverlet INFORMATION Instrumenting module: C:\GitHub\coverlet-examples\artifacts\bin\XUnitProject1.Tests\debug_net10.0\XUnitProject1.Tests.dll
2026-08-20T07:26:53.1616452+00:00 Coverlet TRACE Excluded module filter '[coverlet.*]*'
2026-08-20T07:26:53.1616711+00:00 Coverlet TRACE Excluded module filter '[*.Tests]*'
2026-08-20T07:26:53.1616717+00:00 Coverlet TRACE Excluded module filter '[xunit*]*'
2026-08-20T07:26:53.1808407+00:00 Coverlet TRACE Excluded module: 'C:\GitHub\coverlet-examples\artifacts\bin\XUnitProject1.Tests\debug_net10.0\coverlet.core.dll'
2026-08-20T07:26:53.1808727+00:00 Coverlet TRACE Excluded module: 'C:\GitHub\coverlet-examples\artifacts\bin\XUnitProject1.Tests\debug_net10.0\coverlet.MTP.dll'
2026-08-20T07:26:53.1808756+00:00 Coverlet TRACE Excluded module: 'C:\GitHub\coverlet-examples\artifacts\bin\XUnitProject1.Tests\debug_net10.0\xunit.abstractions.dll'
2026-08-20T07:26:53.1808763+00:00 Coverlet TRACE Excluded module: 'C:\GitHub\coverlet-examples\artifacts\bin\XUnitProject1.Tests\debug_net10.0\xunit.v3.assert.dll'
2026-08-20T07:26:53.1808776+00:00 Coverlet TRACE Excluded module: 'C:\GitHub\coverlet-examples\artifacts\bin\XUnitProject1.Tests\debug_net10.0\xunit.v3.common.dll'
2026-08-20T07:26:53.1808783+00:00 Coverlet TRACE Excluded module: 'C:\GitHub\coverlet-examples\artifacts\bin\XUnitProject1.Tests\debug_net10.0\xunit.v3.core.dll'
2026-08-20T07:26:53.1808839+00:00 Coverlet TRACE Excluded module: 'C:\GitHub\coverlet-examples\artifacts\bin\XUnitProject1.Tests\debug_net10.0\xunit.v3.mtp-v2.dll'
2026-08-20T07:26:53.1808846+00:00 Coverlet TRACE Excluded module: 

[Ksempac]

I'm not OP, but I stumbled upon this thread while dealing with my own coverlet issues, and I believe I know what OP is referring to.

The documentation you mention Bertk offers 2 ways of specifying a config file.

• You rightly mentioned that putting a testconfig.json in a test csproj will make MTP automatically copy it to the output and rename into [appname].testconfig.json, which will then be taken into account
• However, the same documentation also mention if you want to manage your testconfig.json centrally (rather than having one file for each test project of each repository that your CI/CD is building), then it is possible to specify a global file through --config-file option. Ex: dotnet test --solution "mypretty.sln" --coverlet --config-file "/some/path/on/my/hardrive/testconfig.json"

After extensive testing for a day, my own conclusion was that coverlet only supports the first method. On my server:

• Whenever I set a testconfig.json in a test project, I could see that coverlet was following the provided options.
• But when the testconfig.json was specified with --config-file command line, then coverlet behaved like there was no config file.
  • I even confirmed that MTP itself was seeing the file, and was using the options provided inside it (easily provable by setting in the file a new value for the "resultDirectory" option).
  • So only coverlet was ignoring the settings inside the file.

Unfortunately, I do not have the means to provide you with a demonstration of this right away, but I believe it should be fairly easy to test that "--config-file" option on your own.

[Bertk]

@Ksempac Thank you for the detailed information.

Did you also try the MTP central configuration file recommendation Use a centralized testconfig.json?

Add property in test project

<PropertyGroup>
  <TestingPlatformCommandLineArguments>$(TestingPlatformCommandLineArguments) --config-file $(MSBuildThisFileDirectory)testconfig.json</TestingPlatformCommandLineArguments>
</PropertyGroup>

[Ksempac]

@Bertk I'm aware of that third option, but I didn't really try it:

• I did one or two tests, and the whole dotnet test command exploded in my face, so I must have done something wrong with it
• I didn't want to spend more time trying to make it work, because it's not something suited for my use case.
• Because my testing was not as thorough as what I did for the other 2 cases, I cannot say whether coverlet supports this 3rd option.

My use case:
I'm setting up a MTP pipeline for a CI/CD that works across dozens of repositories, and I do not want to have to modify a .sln or several test .csproj to set up my dotnet test command. Also it's likely dotnet test could be run in different circumstances (either on a developer machine, or on different CI/CD, with different underlying OSes), so the path (and possibly the content) could differ significantly.
Hence why I wanted to use the --config-file at the command line level so that each pipeline (or manual call to dotnet test) can provide their testconfig.json using a path that make sense to the underlying CI/CD setup, and with a content that may differs depending on the job. Plus doing it through command line avoids having to modify .sln or .csproj files accross all repositories if something need to be changed.

[Bertk]

@Ksempac Thank you for the feedback. I also use the CLI for my coverlet-examples repository, and today I added a small example demonstrating central configuration.

I also updated the coverlet.MTP documentation with tips for this scenario.

@EraYaN, please close this issue if you have no further questions.

[Ksempac]

@Bertk I looked at your PR, the documentation update and the unit test. This does not solve my use case.

I have dozens of repositories, with hundreds of csproj, on which dozens of developers across different teams work on. And new csproj are created constantly. I do not want to update all csproj files, nor have to constantly check commits to make sure that all newly created csproj files have the required TestingPlatformCommandLineArguments statement.

All of those need to be built from a unique CI/CD using a unique build script. I cannot rely on all developers to know that there need to be a half-hidden TestingPlatformCommandLineArguments statement that need to be added manually in every single csproj. You can be sure at some point that someone will do a basic "add new project", and then not know, or forget, that there needs to be this thing added, and the coverage will be subtly wrong in some way and it will take time to figure out the issue.

What I want to rely on, is the command line in my CI/CD. I want to send:

dotnet test --solution "thesolutionmycicdistryingtobuild.sln" --coverlet --config-file "/some/path/on/my/ci/cd/server/testconfig.json"

and I expect the testconfig.json to be taken into account, with:

• no TestingPlatformCommandLineArguments set in the .sln or .csproj files
• no testconfig.json in the directory containing my solution.
• basically no modification or file that need to be added to every repository I need to build.

The --config-file option is a valid, officially supported, way to provide an external, centrally managed, configuration file for dotnet test with MTP. I think it's reasonable to expect coverlet to support it.

I acknowledge it is possible I did something wrong with my testing, and I do not have an easy reproduction case to upload here. However I did spend significant time on this testing (like I said, i did confirm that MTP itself was seeing my config file).
Did you try it yourself ? Can you use a simple command line with --config-file and see coverlet options being taken into account ?

[Bertk]

@Ksempac I created a README.md that demonstrates use of the --config-file option and documents the observed results when using the CLI. These results were generated with coverlet.MTP version 10.0.2-preview.33.g61d8e1b154.

The --config-file option is an officially supported way to provide an external, centrally managed configuration file to dotnet test when using MTP. It is reasonable to expect Coverlet to support this scenario.

Please note that --testconfig is a Microsoft Testing Platform option, not a Coverlet option. Also, this issue was opened without using the issue template, and the requested validation against the latest nightly build from the current main branch was not performed.

I hope this helps. Please share your results using CLI for '--config-file' option and coverlet.MTP.

[EraYaN]

Alright at least the production version (10.0.1) does not seem to respect the flag.

Some diagnostics snippets:

2026-08-24T08:39:02.9888855+00:00 Microsoft.Testing.Platform.Builder.TestApplication INFORMATION Command line arguments: '--results-directory C:\dev\test-results --config-file C:\dev\testconfig.json --diagnostic --diagnostic-verbosity Trace --coverlet --server dotnettestcli --dotnet-test-pipe testingplatform.pipe.c488e50bb32645e19a27ca5bfc00b34c'
2026-08-24T08:39:02.9893095+00:00 Microsoft.Testing.Platform.Builder.TestApplication DEBUG Machine info:
Machine name: CAL-DEV
OSVersion: Microsoft Windows NT 10.0.26200.0
ProcessorCount: 24
Is64BitOperatingSystem: True
TotalAvailableMemoryBytes(GB): 68

2026-08-24T08:39:02.9893489+00:00 Microsoft.Testing.Platform.Builder.TestApplication INFORMATION TESTINGPLATFORM_DEFAULT_HANG_TIMEOUT: ''
2026-08-24T08:39:03.0111041+00:00 Microsoft.Testing.Platform.Hosts.TestHostBuilder INFORMATION Setting RegisterEnvironmentVariablesConfigurationSource: 'True'
2026-08-24T08:39:03.0145992+00:00 Microsoft.Testing.Platform.Configurations.JsonConfigurationSource+JsonConfigurationProvider INFORMATION Config file 'C:\dev\testconfig.json' loaded.
2026-08-24T08:39:03.0312146+00:00 ConfigurationManager TRACE Configuration file ('C:\dev\testconfig.json') content:
{
  "platformOptions": {
    "Coverlet": {
      "include": "[Calcasa.*]*",
      "exclude": "[coverlet.*]*,[Microsoft.VisualStudio.TestPlatform.*]*,[testhost*]*,[coverlet.*.Tests?]*,[*]Coverlet.Core*,[*]Moq*,[*]TestBase*",
      "excludeByAttribute": "Obsolete,GeneratedCodeAttribute,CompilerGeneratedAttribute,ExcludeFromCodeCoverage,ExcludeFromCodeCoverageAttribute",
      "excludeByFile": "**/*Migrations/*.cs",
      "format": "cobertura,opencover",
      "useSourceLink": false,
      "singleHit": false,
      "includeTestAssembly": false,
      "skipAutoProps": true,
      "deterministicReport": false,
      "excludeAssembliesWithoutSources": "MissingAll"
    }
  }
}

2026-08-24T08:39:03.0321331+00:00 Microsoft.Testing.Platform.Hosts.TestHostBuilder INFORMATION Setting PlatformExitProcessOnUnhandledException: 'False', config file: False environment variable: 
2026-08-24T08:39:03.0568760+00:00 Microsoft.Testing.Platform.Telemetry.TelemetryManager DEBUG TestApplicationOptions.EnableTelemetry: True
2026-08-24T08:39:03.0569891+00:00 Microsoft.Testing.Platform.Telemetry.TelemetryManager DEBUG TESTINGPLATFORM_TELEMETRY_OPTOUT environment variable: ''
2026-08-24T08:39:03.0569998+00:00 Microsoft.Testing.Platform.Telemetry.TelemetryManager DEBUG DOTNET_CLI_TELEMETRY_OPTOUT environment variable: ''
2026-08-24T08:39:03.0570007+00:00 Microsoft.Testing.Platform.Telemetry.TelemetryManager DEBUG Telemetry is 'ENABLED'
2026-08-24T08:39:03.0575259+00:00 Microsoft.Testing.Platform.Telemetry.TelemetryManager DEBUG TESTINGPLATFORM_NOBANNER environment variable: ''
2026-08-24T08:39:03.0575356+00:00 Microsoft.Testing.Platform.Telemetry.TelemetryManager DEBUG DOTNET_NOLOGO environment variable: ''
2026-08-24T08:39:03.0632668+00:00 Microsoft.Testing.Platform.Telemetry.TelemetryManager DEBUG Telemetry collector provider: 'Microsoft.Testing.Extensions.Telemetry.AppInsightsProvider'
2026-08-24T08:39:03.0810930+00:00 Microsoft.Testing.Extensions.TrxReport.Abstractions.TrxEnvironmentVariableProvider TRACE TRX pipe name: 'testingplatform.pipe.47b936ea52a54ed4b74e6699e066a7a3
2026-08-24T08:39:03.0830155+00:00 Coverlet TRACE [DIAG] CoverletExtensionCollector constructor - running in controller process
2026-08-24T08:39:03.0830248+00:00 Coverlet TRACE [DIAG]   Process ID: 63700
2026-08-24T08:39:03.0833947+00:00 Microsoft.Testing.Extensions.TrxReport.Abstractions.TrxProcessLifetimeHandler TRACE TRX pipe name: 'testingplatform.pipe.47b936ea52a54ed4b74e6699e066a7a3
2026-08-24T08:39:03.0918276+00:00 Microsoft.Testing.Extensions.Telemetry.AppInsightsProvider TRACE Send telemetry event: dotnet/testingplatform/host/testhostbuilt
    native aot: false
    hot reload: false
    version: 2.3.3+44aa76e6a61d4908f06dfd77a51d4b7e3e7ce40f
    testhost: 3c0a042a19ba9bbffedab53106b753999a20720bfd8f0d2c95dae6f17b6d6a95
    framework: .NET 10.0.11
    architecture: X64
    os architecture: X64
    os: Microsoft Windows 10.0.26200
    runtime: win-x64
    debug build: false
    debugger attached: false
    application mode: TestHostControllers
    telemetry version: 20
    session id: efd7bf3a-a67b-4295-9d26-d0b32c734b53
    reporter id: ea922961-ca3c-429a-8f6d-9fbaff11abf0
    is ci: false
    create builder start: 1787560742964680192.00
    build builder start: 1787560743009938176.00
    build builder stop: 1787560743089138176.00
    create builder stop: 1787560743089138176.00

2026-08-24T08:39:03.1045237+00:00 Microsoft.Testing.Platform.Hosts.TestHostControllersTestHost DEBUG Test host controller process info: Process: C:\dev\net10.0\Calcasa.BusinessRules.Tests.exe, Arguments: --results-directory C:\dev\test-results --config-file C:\dev\testconfig.json --diagnostic --diagnostic-verbosity Trace --coverlet --server dotnettestcli --dotnet-test-pipe testingplatform.pipe.c488e50bb32645e19a27ca5bfc00b34c, Workspace: C:\dev\net10.0
2026-08-24T08:39:03.1045420+00:00 Microsoft.Testing.Platform.Hosts.TestHostControllersTestHost DEBUG TESTINGPLATFORM_TESTHOSTCONTROLLER_CORRELATIONID_63700 '67f51c1f3d6a498a99d77e014e971211'
2026-08-24T08:39:03.1079249+00:00 coverlet.MTP.EnvironmentVariables.CoverletExtensionEnvironmentVariableProvider DEBUG [CoverletEnvVarProvider] Set COVERLET_MTP_COVERAGE_ENABLED=true
2026-08-24T08:39:03.1095389+00:00 Coverlet TRACE === BeforeTestHostProcessStartAsync START ===
2026-08-24T08:39:03.1095563+00:00 Coverlet TRACE Controller PID: 63700
2026-08-24T08:39:03.1095589+00:00 Coverlet TRACE Coverage enabled (--coverlet flag): True
2026-08-24T08:39:03.1100705+00:00 Coverlet TRACE No testconfig.json found for module: C:\dev\net10.0\Calcasa.BusinessRules.Tests.dll
2026-08-24T08:39:03.1100799+00:00 Coverlet TRACE   Searched: Calcasa.BusinessRules.Tests.testconfig.json, testconfig.json
2026-08-24T08:39:03.1111268+00:00 Coverlet TRACE Configuration file not found: C:\dev\net10.0\coverlet.mtp.appsettings.json
2026-08-24T08:39:03.1113172+00:00 CollectorExtension DEBUG [Default] coverlet-deterministic-report: False
2026-08-24T08:39:03.1118244+00:00 CollectorExtension DEBUG [Default] coverlet-exclude-by-attribute: ExcludeFromCodeCoverage, ExcludeFromCodeCoverageAttribute, GeneratedCodeAttribute, CompilerGeneratedAttribute
2026-08-24T08:39:03.1119392+00:00 CollectorExtension DEBUG [Default] coverlet-exclude: [coverlet.*]*, [xunit.*]*, [NUnit3.*]*, [nunit.*]*, [Microsoft.Testing.*]*, [Microsoft.Testplatform.*]*, [Microsoft.VisualStudio.TestPlatform.*]*, [MSTest*]*, [testhost*]*
2026-08-24T08:39:03.1121588+00:00 CollectorExtension DEBUG [Default] coverlet-include-test-assembly: False
2026-08-24T08:39:03.1122125+00:00 CollectorExtension DEBUG [Default] coverlet-single-hit: False
2026-08-24T08:39:03.1122465+00:00 CollectorExtension DEBUG [Default] coverlet-skip-auto-props: False
2026-08-24T08:39:03.1123121+00:00 CollectorExtension DEBUG [Default] coverlet-output-format: json, cobertura

And it does in fact not load the config unless I copy it to the C:\dev\net10.0 folder. I have tried both the Exclude and exclude versions, it seems to not have any impact. If I copy the file to the output folder like this the lowerCamelCase version works just fine.

<ItemGroup>
  <!-- TODO Remove when coverlet respects config-file switch -->
  <Content Include="$(MSBuildThisFileDirectory)/../testconfig.json" Link="testconfig.json">
    <CopyToOutputDirectory>Always</CopyToOutputDirectory>
  </Content>
</ItemGroup>

I can't seem to find an active feed with the listed preview version. I also didn't use the issue template since I thought I was doing a feature request. I have added the information to the original question.