Add Code coverage report (#79)

Add code coverage report to pipeline. Fixes #42.

Design is basically:

1. Capture code coverage files in `test.runsettings` to avoid embedding
settings / logic in the pipeline YAML and make it possible to generate
coverage locally the same as CI
- Currently uses a simple assembly include limited to
`Moq.Analyzers.dll`. Ideally we could say "all project references".
Added a TODO for that, as well as to discuss with the code coverage team
3. Add `CleanCoverageReport` and `GenerateCoverageReport` targets in
test MSBuild slice to handle merging the reports across test projects
4. Use the MSBuild task for `dotnet-reportgenerator` to merge code
coverage reports into:
    - A markdown summary for GitHub
    - An HTML report with line-coverage info
    - A merged Cobertura XML report for tool processing
5. Update GitHub Actions YAML so that:
    - Markdown summary is added to the summary of the run
    - Other coverage reports are added as a build artifact

I didn't add any functionality to fail below a certain threshold, as
tools generally use a static threshold, or do odd things to smuggle
state like creating a branch in the repo or storing information in a
gist, so leaving that for later.

.github/workflows/main.yml

@@ -56,23 +56,34 @@ jobs:
       run: dotnet build --no-restore --configuration Release /bl:./artifacts/logs/release/build.release.binlog
 
     - name: Test
-      run: dotnet test --no-build --configuration Release
+      run: dotnet test --no-build --configuration Release --settings ./build/targets/tests/test.runsettings
 
-    - name: Publish Test Report
+    - name: Upload *.received.* files
+      uses: actions/upload-artifact@v4
+      if: failure()
+      with:
+        name: verify-test-results
+        path: |
+          **/*.received.*
+
+    - name: Upload Test Report
       uses: actions/upload-artifact@v4
       if: success() || failure()
       with:
         name: .NET Test Reports (${{ matrix.os }})
         path: "artifacts/TestResults/**/*.trx"
         if-no-files-found: error
 
-    - name: Upload Test Results
-      uses: actions/upload-artifact@v2
-      if: failure()      
+    - name: Upload Code Coverage Report
+      uses: actions/upload-artifact@v4
+      if: success() || failure()
       with:
-        name: verify-test-results
-        path: |
-          **/*.received.*
+        name: .NET Code Coverage Reports (${{ matrix.os }})
+        path: "artifacts/TestResults/coverage/**"
+
+    - name: Publish coverage summary
+      run: cat artifacts/TestResults/coverage/SummaryGithub.md >> $GITHUB_STEP_SUMMARY
+      shell: bash
 
     - name: Upload binlogs
       uses: actions/upload-artifact@v4

build/targets/tests/Packages.props

@@ -1,5 +1,6 @@
 <Project>
   <ItemGroup>
+    <PackageVersion Include="ReportGenerator" Version="5.3.6" />
     <PackageVersion Include="Microsoft.CodeAnalysis.CSharp.Analyzer.Testing" Version="1.1.2-beta1.24273.1" />
     <PackageVersion Include="Microsoft.CodeAnalysis.CSharp.CodeFix.Testing" Version="1.1.2-beta1.24273.1" />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.10.0" />

build/targets/tests/Tests.props

@@ -1,5 +1,6 @@
 <Project>
   <ItemGroup Condition=" '$(IsTestProject)' == 'true' ">
+    <PackageReference Include="ReportGenerator" />
     <PackageReference Include="Meziantou.Xunit.ParallelTestFramework" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" />
     <PackageReference Include="xunit" />

build/targets/tests/Tests.targets

@@ -3,5 +3,28 @@
     <!-- Enable test logging to TRX files and place them in the artifacts directory -->
     <VSTestLogger>trx%3bLogFileName=$(MSBuildProjectName).trx</VSTestLogger>
     <VSTestResultsDirectory Condition="'$(VSTestResultsDirectory)' == ''">$(ArtifactsTestResultsPath)/$(TargetFramework)</VSTestResultsDirectory>
+
+    <_TestCoverageGlob>$(ArtifactsTestResultsPath)/**/*.cobertura.xml</_TestCoverageGlob>
+    <_TestCoverageReportDirectory>$(ArtifactsTestResultsPath)/coverage</_TestCoverageReportDirectory>
   </PropertyGroup>
+
+  <Target Name="CleanCoverageReport" BeforeTargets="Test;VSTest" Condition=" '$(IsTestProject)' == 'true' ">
+    <!-- Prevent this previous runs' coverage files from being merged into this report run. -->
+    <RemoveDir Directories="$(_TestCoverageReportDirectory)" />
+
+    <ItemGroup>
+      <_CoverageFiles Include="$(_TestCoverageGlob)" />
+    </ItemGroup>
+    <Delete Files="@(_CoverageFiles)" />
+    <ItemGroup>
+      <_CoverageFiles Remove="@(_CoverageFiles)" />
+    </ItemGroup>
+  </Target>
+
+  <Target Name="GenerateCoverageReport" AfterTargets="Test;VSTest" Condition=" '$(IsTestProject)' == 'true' ">
+    <ItemGroup>
+      <_CoverageFiles Include="$(_TestCoverageGlob)" />
+    </ItemGroup>
+    <ReportGenerator ProjectDirectory="$(MSBuildProjectDirectory)" ReportFiles="@(_CoverageFiles)" TargetDirectory="$(_TestCoverageReportDirectory)" ReportTypes="MarkdownSummaryGithub;Cobertura;HtmlInline" />
+  </Target>
 </Project>

build/targets/tests/test.runsettings

@@ -0,0 +1,28 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- File name extension must be .runsettings -->
+<RunSettings>
+  <DataCollectionRunSettings>
+    <DataCollectors>
+      <DataCollector friendlyName="Code Coverage" uri="datacollector://Microsoft/CodeCoverage/2.0" assemblyQualifiedName="Microsoft.VisualStudio.Coverage.DynamicCoverageDataCollector, Microsoft.VisualStudio.TraceCollector, Version=11.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a">
+        <Configuration>
+          <Format>cobertura</Format>
+          <IncludeTestAssembly>False</IncludeTestAssembly>
+          <CodeCoverage>
+            <EnableStaticNativeInstrumentation>False</EnableStaticNativeInstrumentation>
+            <EnableDynamicNativeInstrumentation>False</EnableDynamicNativeInstrumentation>
+            <ModulePaths>
+              <Include>
+                <!--
+                  Limit code coverage to the shipping binary.
+                  TODO: Consider using a "Just my code"-esque tool to automatically include all project references.
+                  Discuss in https://github.com/microsoft/codecoverage.
+                -->
+                <ModulePath>.*Moq\.Analyzers\.dll$</ModulePath>
+              </Include>
+            </ModulePaths>
+          </CodeCoverage>
+        </Configuration>
+      </DataCollector>
+    </DataCollectors>
+  </DataCollectionRunSettings>
+</RunSettings>