Collect default code coverage

You collect code coverage by passing --collect "Code coverage" to your dotnet test command line, e.g.:

dotnet test .\MyProject.UnitTests\MyProject.UnitTests.csproj --collect "Code coverage"

This generates a .coverage file, which is a proprietary binary format that's only viewable in Visual Studio Enterprise.

Problems when collecting code coverage

• Coverage being collected for third party libraries you don't control
• Coverage being collected for unit tests themselves
• Potential issues with coverage then being collected for dynamically generated fakes, such as those by Moq
• Coverage being collected for generated code or internals
• Hard to diagnose what is being collected (or not collected) if you don't have Visual Studio Enterprise

Configuring Code Coverage

You can configure Code Coverage by using a .runsettings file.

This is an XML configuration file, and there is no longer built-in support for editing this in Visual Studio so you must edit it by hand.

Recommendations

• Add a .runsettings file for code coverage
• Make sure you set mergeDefaults to false for the ModulePaths, and then explicitly add the patterns for matching your included and excluded files.
• The included pattern doesn't seem to be reliable, so you will likely need to add a lot of exclusions for libraries such as Moq, and to exclude your Unit Test and Integration Test projects.
• The module paths may be normalized to lower case, so the regex should be lower case too.
• Add exclusions to the Sources for boilerplate or high-level files that don't need coverage e.g. Startup.cs, Global.asax.cs
• Use ReportGenerator to generate viewable output that can also be integrated easily into your CI/CD pipeline, so everyone can get visibility on your code coverage
• Add various unit testing framework attributes to the ignore lists

.runsettings Boilerplate

<?xml version="1.0" encoding="UTF-8"?>
<RunSettings>
    <RunConfiguration>
        <ResultsDirectory>.\TestResults</ResultsDirectory>
        <EnvironmentVariables>
            <!-- List of environment variables we want to set-->
            <!-- <DOTNET_ROOT>C:\ProgramFiles\dotnet</DOTNET_ROOT> -->
        </EnvironmentVariables>
    </RunConfiguration>
    <DataCollectionRunSettings>
        <DataCollectors>
            <DataCollector friendlyName="Code Coverage" uri="datacollector://Microsoft/CodeCoverage/2.0">
                <Configuration>
                    <CodeCoverage>
                        <ModulePaths mergeDefaults="false">
                              <Include>
                                <ModulePath>.*MyProject.*\.dll$</ModulePath>
                                <ModulePath>.*\.exe$</ModulePath>
                            </Include>
                            <Exclude>
                                <ModulePath>.*TestAdapter.*</ModulePath>
                                <ModulePath>.*NUnit.*</ModulePath>
                                <ModulePath>.*\\moq\.dll$</ModulePath>
                                <ModulePath>.*\\fluentvalidation\.dll$</ModulePath>
                                <ModulePath>.*\\MyCompany\.MyProject\.unittests\.dll</ModulePath>
                                <ModulePath>.*(unit|integration)tests\.dll</ModulePath>
                                <ModulePath>.*CodeCoverage.exe$</ModulePath>
                                <ModulePath>.*\Coverlet.Collector.dll$</ModulePath>
                                <ModulePath>.*\Coverlet.Core.dll$</ModulePath>
                            </Exclude>
                        </ModulePaths>
            <Sources>
              <Exclude>
                <Source>.*\\Program.cs$</Source>
                <Source>.*\\Startup.cs$</Source>
                <Source>.*\\Global.asax.cs$</Source>
              </Exclude>
            </Sources>
            <UseVerifiableInstrumentation>True</UseVerifiableInstrumentation>
            <AllowLowIntegrityProcesses>True</AllowLowIntegrityProcesses>
            <CollectFromChildProcesses>True</CollectFromChildProcesses>
            <CollectAspDotNet>false</CollectAspDotNet>
          </CodeCoverage>
                </Configuration>
            </DataCollector>
            <!-- Configuration for blame data collector -->
            <DataCollector friendlyName="blame" enabled="True">
            </DataCollector>
        </DataCollectors>
    </DataCollectionRunSettings>
    <LoggerRunSettings>
        <Loggers>
            <Logger friendlyName="console" enabled="True">
                <Configuration>
                    <Verbosity>quiet</Verbosity>
                </Configuration>
            </Logger>
            <Logger friendlyName="trx" enabled="True"/>
        </Loggers>
    </LoggerRunSettings>
</RunSettings>

References

• Use code coverage to determine how much code is being tested
• VSTest Platform
• dotnet test
• RunSettings arguments
• Coverlet coverage tool
• Reviewing code coverage results in Azure DevOps
• ReportGenerator Integration
• VSTest Console Options
• Default configuration