[BUG] Code coverage file not generated with OpenCover / XUnit

[SaxoLigtorn]

Describe the bug
No coverage file is generated, as it should

To Reproduce
run the following command in the tests folder
dotnet test --coverlet --coverlet-output-format opencover --results-directory ./TestResults -diagnostic --configuration Debug --diagnostic-verbosity trace

Expected behavior
An OpenCover coverage file should be generated

Actual behavior
The command runs with success, but nothing is created. The diagnostic file showns the following

2026-04-14T15:08:00.0193419+00:00 Coverlet TRACE Coverage enabled (--coverlet flag): True
2026-04-14T15:08:00.0196161+00:00 Coverlet ERROR Could not determine test module path. Coverage disabled.

Configuration (please complete the following information):
Please provide more information on your .NET configuration:
* coverlet.MTP 8.0.1
* Microsoft.Testing.Platform 2.2.1
* xunit.v3.mtp-v2 3.2.2

.NET: net10.0
OS: Windows 24H2
Architecture: AnyCPU

❗ Please also read Known Issues

[SaxoLigtorn]

A test solution which have the issue, and it also includes the diagnostic files
TestMTP.zip

[Bertk]

Thank you for your request! I have an example repository that is quite similar to your setup.

To help investigate, I created a simplified version of your repository with a few adjustments: coverlet-issue-1892.zip
. In this version, I also updated to the newer coverlet.MTP package from the Coverlet nightly build feed.

Using the following command:

dotnet test --project tests\Project1.Tests\Project1.Tests.csproj --report-xunit-trx --framework net10.0 --verbosity normal --coverlet --coverlet-output-format opencover --diagnostic --diagnostic-verbosity trace --diagnostic-file-prefix issue1892

the tests run successfully and produce the expected results:

  Project1 net10.0 succeeded (2,6s) → src\Project1\bin\Debug\net10.0\Project1.dll
  Project1.Tests net10.0 succeeded (1,1s) → tests\Project1.Tests\bin\Debug\net10.0\Project1.Tests.dll

Build succeeded in 4,2s
Running tests from tests\Project1.Tests\bin\Debug\net10.0\Project1.Tests.dll (net10.0|x64)
tests\Project1.Tests\bin\Debug\net10.0\Project1.Tests.dll (net10.0|x64) passed (535ms)

  In process file artifacts produced:
    - tests\Project1.Tests\bin\Debug\net10.0\TestResults\bertk_LAPTOP-BERT_2026-04-15_13_35_20.190780.trx

Test run summary: Passed!
  total: 5
  failed: 0
  succeeded: 5
  skipped: 0
  duration: 3s 334ms

<?xml version="1.0" encoding="utf-8"?>
<CoverageSession>
  <Summary numSequencePoints="15" visitedSequencePoints="15" numBranchPoints="2" visitedBranchPoints="2" sequenceCoverage="100" branchCoverage="100" maxCyclomaticComplexity="5" minCyclomaticComplexity="5" visitedClasses="1" numClasses="1" visitedMethods="4" numMethods="4" />
  <Modules>
    <Module hash="234A9E9F-2456-4605-A8A5-F6C21E02933C">
      <ModulePath>Project1.dll</ModulePath>
      <ModuleTime>2026-04-15T01:35:20</ModuleTime>
      <ModuleName>Project1</ModuleName>
      <Files>
        <File uid="1" fullPath="C:\GitHub\coverlet-issue-1892\src\Project1\Calculator.cs" />
      </Files>
      <Classes>
        <Class>
          <Summary numSequencePoints="15" visitedSequencePoints="15" numBranchPoints="2" visitedBranchPoints="2" sequenceCoverage="100" branchCoverage="100" maxCyclomaticComplexity="2" minCyclomaticComplexity="1" visitedClasses="1" numClasses="1" visitedMethods="4" numMethods="4" />
          <FullName>Project1.Calculator</FullName>
          <Methods>
            <Method cyclomaticComplexity="1" nPathComplexity="1" sequenceCoverage="100" branchCoverage="100" isConstructor="False" isGetter="False" isSetter="False" isStatic="True">
              <Summary numSequencePoints="3" visitedSequencePoints="3" numBranchPoints="0" visitedBranchPoints="0" sequenceCoverage="100" branchCoverage="100" maxCyclomaticComplexity="1" minCyclomaticComplexity="1" visitedClasses="0" numClasses="0" visitedMethods="1" numMethods="1" />
              <MetadataToken />
              <Name>System.Int32 Project1.Calculator::Add(System.Int32,System.Int32)</Name>
              <FileRef uid="1" />
              <SequencePoints>
                <SequencePoint vc="1" uspid="8" ordinal="0" sl="8" sc="1" el="8" ec="2" bec="0" bev="0" fileid="1" />
                <SequencePoint vc="1" uspid="9" ordinal="1" sl="9" sc="1" el="9" ec="2" bec="0" bev="0" fileid="1" />
                <SequencePoint vc="1" uspid="10" ordinal="2" sl="10" sc="1" el="10" ec="2" bec="0" bev="0" fileid="1" />
              </SequencePoints>
              <BranchPoints />
              <MethodPoint vc="3" uspid="0" p8:type="SequencePoint" ordinal="0" offset="0" sc="0" sl="8" ec="1" el="10" bec="0" bev="0" fileid="1" xmlns:p8="xsi" />
            </Method>
            <Method cyclomaticComplexity="1" nPathComplexity="1" sequenceCoverage="100" branchCoverage="100" isConstructor="False" isGetter="False" isSetter="False" isStatic="True">
              <Summary numSequencePoints="3" visitedSequencePoints="3" numBranchPoints="0" visitedBranchPoints="0" sequenceCoverage="100" branchCoverage="100" maxCyclomaticComplexity="1" minCyclomaticComplexity="1" visitedClasses="0" numClasses="0" visitedMethods="1" numMethods="1" />
              <MetadataToken />
              <Name>System.Int32 Project1.Calculator::Subtract(System.Int32,System.Int32)</Name>
              <FileRef uid="1" />
              <SequencePoints>
                <SequencePoint vc="1" uspid="13" ordinal="0" sl="13" sc="1" el="13" ec="2" bec="0" bev="0" fileid="1" />
                <SequencePoint vc="1" uspid="14" ordinal="1" sl="14" sc="1" el="14" ec="2" bec="0" bev="0" fileid="1" />
                <SequencePoint vc="1" uspid="15" ordinal="2" sl="15" sc="1" el="15" ec="2" bec="0" bev="0" fileid="1" />
              </SequencePoints>
              <BranchPoints />
              <MethodPoint vc="3" uspid="0" p8:type="SequencePoint" ordinal="1" offset="1" sc="0" sl="13" ec="1" el="15" bec="0" bev="0" fileid="1" xmlns:p8="xsi" />
            </Method>
            <Method cyclomaticComplexity="1" nPathComplexity="1" sequenceCoverage="100" branchCoverage="100" isConstructor="False" isGetter="False" isSetter="False" isStatic="True">
              <Summary numSequencePoints="3" visitedSequencePoints="3" numBranchPoints="0" visitedBranchPoints="0" sequenceCoverage="100" branchCoverage="100" maxCyclomaticComplexity="1" minCyclomaticComplexity="1" visitedClasses="0" numClasses="0" visitedMethods="1" numMethods="1" />
              <MetadataToken />
              <Name>System.Int32 Project1.Calculator::Multiply(System.Int32,System.Int32)</Name>
              <FileRef uid="1" />
              <SequencePoints>
                <SequencePoint vc="1" uspid="18" ordinal="0" sl="18" sc="1" el="18" ec="2" bec="0" bev="0" fileid="1" />
                <SequencePoint vc="1" uspid="19" ordinal="1" sl="19" sc="1" el="19" ec="2" bec="0" bev="0" fileid="1" />
                <SequencePoint vc="1" uspid="20" ordinal="2" sl="20" sc="1" el="20" ec="2" bec="0" bev="0" fileid="1" />
              </SequencePoints>
              <BranchPoints />
              <MethodPoint vc="3" uspid="0" p8:type="SequencePoint" ordinal="2" offset="2" sc="0" sl="18" ec="1" el="20" bec="0" bev="0" fileid="1" xmlns:p8="xsi" />
            </Method>
            <Method cyclomaticComplexity="2" nPathComplexity="2" sequenceCoverage="100" branchCoverage="100" isConstructor="False" isGetter="False" isSetter="False" isStatic="True">
              <Summary numSequencePoints="6" visitedSequencePoints="6" numBranchPoints="2" visitedBranchPoints="2" sequenceCoverage="100" branchCoverage="100" maxCyclomaticComplexity="2" minCyclomaticComplexity="2" visitedClasses="0" numClasses="0" visitedMethods="1" numMethods="1" />
              <MetadataToken />
              <Name>System.Int32 Project1.Calculator::Divide(System.Int32,System.Int32)</Name>
              <FileRef uid="1" />
              <SequencePoints>
                <SequencePoint vc="2" uspid="23" ordinal="0" sl="23" sc="1" el="23" ec="2" bec="0" bev="0" fileid="1" />
                <SequencePoint vc="2" uspid="24" ordinal="1" sl="24" sc="1" el="24" ec="2" bec="2" bev="2" fileid="1" />
                <SequencePoint vc="1" uspid="25" ordinal="2" sl="25" sc="1" el="25" ec="2" bec="0" bev="0" fileid="1" />
                <SequencePoint vc="1" uspid="26" ordinal="3" sl="26" sc="1" el="26" ec="2" bec="0" bev="0" fileid="1" />
                <SequencePoint vc="1" uspid="29" ordinal="4" sl="29" sc="1" el="29" ec="2" bec="0" bev="0" fileid="1" />
                <SequencePoint vc="1" uspid="30" ordinal="5" sl="30" sc="1" el="30" ec="2" bec="0" bev="0" fileid="1" />
              </SequencePoints>
              <BranchPoints>
                <BranchPoint vc="1" uspid="24" ordinal="0" path="0" offset="7" offsetend="9" sl="24" fileid="1" />
                <BranchPoint vc="1" uspid="24" ordinal="1" path="1" offset="7" offsetend="21" sl="24" fileid="1" />
              </BranchPoints>
              <MethodPoint vc="6" uspid="0" p8:type="SequencePoint" ordinal="3" offset="3" sc="0" sl="23" ec="1" el="30" bec="0" bev="0" fileid="1" xmlns:p8="xsi" />
            </Method>
          </Methods>
        </Class>
      </Classes>
    </Module>
  </Modules>
</CoverageSession>

Additionally, the Coverlet code coverage file in OpenCover format is generated correctly (see snippet above).

I haven’t yet analyzed in detail why your original repository is not working as expected. However, with the attached sample and by updating to the latest nightly build coverlet.MTP version, you should be able to verify the current behavior and compare it with your setup.

Please let me know if you’re still seeing issues after trying this.

[SaxoLigtorn]

You example worked fine, so I used that to compare the two solutions and eventually found the issue. it turns out that Coverlet doesn't like projects starting with Dotnet. E.g. if you rename your Project1.Tests.csproj to Dotnet.Tests.csproj, you should get the same issue

I have a suspicion that it is caused by this code

coverlet/src/coverlet.MTP/Collector/CollectorExtension.cs

Line 592 in 0cb97f0

!fileName.StartsWith("dotnet", StringComparison.OrdinalIgnoreCase))

[Bertk]

Thank you for the information. I removed the obsolete filter from prototyping phase.