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VSTestIntegration.md

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Coverlet integration with VSTest (a.k.a. Visual Studio Test Platform)

At the moment collectors integration supports only .NET Core applications and not .NET Framework ones.

As explained in quick start section to use collectors you need to run SDK v2.2.401 or newer and your project file must reference coverlet.collector.dll and a minimum version of Microsoft.NET.Test.Sdk.
A sample project file looks like:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFrameworks>netcoreapp3.0;netcoreapp2.1;net46</TargetFrameworks>
  </PropertyGroup>
  <ItemGroup>
    <!-- Minimum version 16.5.0 -->
    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.5.0" />
    <!-- Update this reference when new version is released -->
    <PackageReference Include="coverlet.collector" Version="1.2.0">
      <PrivateAssets>all</PrivateAssets>
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
    </PackageReference>
  ...
  </ItemGroup>
...
</Project>

The reference to coverlet.collector package is included by default with xunit template test (dotnet new xunit), you only need to update the package for new versions like any other package reference.

With correct reference in place you can run coverage through default dotnet test CLI verbs:

dotnet test --collect:"XPlat Code Coverage"

or

dotnet publish
...
  ... -> C:\project\bin\Debug\netcoreapp3.0\testdll.dll
  ... -> C:\project\bin\Debug\netcoreapp3.0\publish\
...
dotnet vstest C:\project\bin\Debug\netcoreapp3.0\publish\testdll.dll --collect:"XPlat Code Coverage"

As you can see in case of vstest verb you must publish project before.

At the end of tests you'll find the coverage file data under default vstest plat directory TestResults

Attachments:
  C:\git\coverlet\Documentation\Examples\VSTest\HelloWorld\XUnitTestProject1\TestResults\bc5e983b-d7a8-4f17-8c0a-8a8831a4a891\coverage.cobertura.xml
Test Run Successful.
Total tests: 1
     Passed: 1
 Total time: 2,5451 Seconds

You can change the position of files using standard dotnet test switch [-r|--results-directory]
NB: By design vstest platform will create your file under a random named folder(guid string) so if you need stable path to load file to some gui report system(i.e. coveralls, codecov, reportgenerator etc..) that doesn't support glob patterns or hierarchical search, you'll need to manually move resulting file to a predictable folder

Coverlet options supported by VSTest integration

At the moment VSTest integration doesn't support all features of msbuild and .NET tool, for instance show result on console, report merging and threshold validation. We're working to fill the gaps.
PS: if you don't have any other way to merge reports(for instance your report generator doesn't support multi coverage file) you can for the moment exploit a trick reported by one of our contributor Daniel Paz(@p4p3) coverlet-coverage#225 (comment)

Default option (if you don't specify a runsettings file)

Option Summary
Format Results format in which coverage output is generated. Default format is cobertura. Supported format lcov, opencover, cobertura, teamcity, json (default coverlet proprietary format)

Advanced Options (Supported via runsettings)

These are a list of options that are supported by coverlet. These can be specified as datacollector configurations in the runsettings.

Option Summary
Format Coverage output format. These are either cobertura, json, lcov, opencover or teamcity as well as combinations of these formats.
Exclude Exclude from code coverage analysing using filter expressions.
ExcludeByFile Ignore specific source files from code coverage.
Include Explicitly set what to include in code coverage analysis using filter expressions.
IncludeDirectory Explicitly set which directories to include in code coverage analysis.
SingleHit Specifies whether to limit code coverage hit reporting to a single hit for each location.
UseSourceLink Specifies whether to use SourceLink URIs in place of file system paths.
IncludeTestAssembly Include coverage of the test assembly.

How to specify these options via runsettings?

<?xml version="1.0" encoding="utf-8" ?>
<RunSettings>
  <DataCollectionRunSettings>
    <DataCollectors>
      <DataCollector friendlyName="XPlat code coverage">
        <Configuration>
          <Format>json,cobertura,lcov,teamcity,opencover</Format>          
          <Exclude>[coverlet.*.tests?]*,[*]Coverlet.Core*</Exclude> <!-- [Assembly-Filter]Type-Filter -->
          <Include>[coverlet.*]*,[*]Coverlet.Core*</Include> <!-- [Assembly-Filter]Type-Filter -->
          <ExcludeByAttribute>Obsolete,GeneratedCodeAttribute,CompilerGeneratedAttribute</ExcludeByAttribute>
          <ExcludeByFile>**/dir1/class1.cs,**/dir2/*.cs,**/dir3/**/*.cs,</ExcludeByFile> <!-- Globbing filter -->
          <IncludeDirectory>../dir1/,../dir2/,</IncludeDirectory>
          <SingleHit>false</SingleHit>
          <UseSourceLink>true</UseSourceLink>
          <IncludeTestAssembly>true</IncludeTestAssembly>
        </Configuration>
      </DataCollector>
    </DataCollectors>
  </DataCollectionRunSettings>
</RunSettings>

Filtering details are present on msbuild guide.

This runsettings file can easily be provided using command line option as given :

  1. dotnet test --collect:"XPlat Code Coverage" --settings coverlet.runsettings

  2. dotnet vstest C:\project\bin\Debug\netcoreapp3.0\publish\testdll.dll --collect:"XPlat Code Coverage" --settings coverlet.runsettings

Take a look at our HelloWorld sample.

Passing runsettings arguments through commandline

You can avoid to pass runsettings file to dotnet test driver and use the xml flat syntax command line.
For instance if you want to set the Format element runsettings option you can use this syntax

dotnet test --collect:"XPlat Code Coverage" -- DataCollectionRunSettings.DataCollectors.DataCollector.Configuration.Format=json,cobertura,lcov,teamcity,opencover

Take a look here for further informations https://github.com/microsoft/vstest-docs/blob/master/docs/RunSettingsArguments.md

How it works

Coverlet integration is implemented with the help of datacollectors.
When we specify --collect:"XPlat Code Coverage" vstest platform tries to load coverlet collectors inside coverlet.collector.dll

  1. Outproc Datacollector : The outproc collector run in a separate process(datacollector.exe/datacollector.dll) than the process in which tests are being executed(testhost*.exe/testhost.dll). This datacollector is responsible for calling into coverlet APIs for instrumenting dlls, collecting coverage results and sending the coverage output file back to test platform.

  2. Inproc Datacollector : The inproc collector is loaded in the testhost process executing the tests. This collector will be needed to remove the dependency on the process exit handler to flush the hit files and avoid to hit this serious known issue

Known Issues

For a comprehensive list of known issues check the detailed documentation https://github.com/tonerdo/coverlet/blob/master/Documentation/KnownIssues.md