Code coverage is the percentage of code that is covered by automated tests.  As part of your CI builds, you should add a report that shows the coverage so you can track it as it goes up (of course).

Adding code coverage to your CI build is as simple as adding a new task to your build script.  In other posts we’ve shown creating build scripts with various technologies.  Here we’ll show adding a psake task that to invoke code coverage.

task CodeCoverage {
    Write-Host("##[section]Starting: Build task 'CodeCoverage'")
    copy_all_assemblies_for_test $test_dir
    exec {
        & $vstest_dir\vstest.console.exe $test_dir\$unitTestAssembly $test_dir\$integrationTestAssembly /TestAdapterPath:$test_dir /Logger:trx /Enablecodecoverage /Settings:$source_dir\CodeCoverage.runSettings
    }
    Write-Host("##[section]Finishing: Build task 'CodeCoverage'")
}

The line with vstest.console.exe does the real work.  It is also used for running tests and in this case, we’re passing in the /Enablecodecoverage /Settings:$source_dir\CodeCoverage.runSettings parameters to get a .coverage file output.  The first parameter is obvious, the second one specifies a file to customize the code coverage analysis.  Typically, you don’t need one of these, but in this case we had some test assemblies to exclude as shown below. (You can also exclude with the 
ExcludeFromCodeCoverage C# class attribute).

<!-- Match assembly file paths: -->
<ModulePaths>
	<Include>
		<ModulePath>.*\.dll$</ModulePath>
		<ModulePath>.*\.exe$</ModulePath>
	</Include>
	<Exclude>
		<ModulePath>.*CPPUnitTestFramework.*</ModulePath>
                <!-- these three lines were added -->
		<ModulePath>.*UnitTests.*</ModulePath>
		<ModulePath>.*IntegrationTests.*</ModulePath>
		<ModulePath>.*SmokeTests.*</ModulePath>
	</Exclude>
</ModulePaths>

In your Azure DevOps build pipeline, add a
Publish Test Results
 task after the build step, if you don’t already have one.  In the
Test results files
  control for that task, add the .coverage file to get it copied, too.

*.trx
***.coverage

Viewing a .coverage File

Once you build successfully, there will be a Code Coverage tab for your build.  Currently all you can do is download the file. 

Download the file, and open the solution that was built in VS2017, and open the .coverage file in VS2017.  You should then see a Code Coverage Results  window open up.

From here you can view your coverage by assembly and drill into each one to open up the source code.  The selected toggle in the tool bar above is  Show Code Coverage Coloring that puts different colors on source code depending on its coverage (if you click on it from that window, not just opening the file).

Accessing Code Coverage via REST

The Azure DevOps REST interface has a method to get the code coverage data programmatically.  The flags indicate what level of detail you want to get back (1 for modules in this example).  Documentation for this call is here.

$encodedPat = [System.Convert]::ToBase64String([System.Text.Encoding]::UTF8.GetBytes(":$PAT"))
$headers =  @{Authorization="Basic $encodedPat";Accept="application/json" }

$coverage = Invoke-RestMethod -Uri "https://dev.azure.com/project0795/CmBootcamp/_apis/test/codecoverage?buildId=11&flags=1&api-version=5.0-preview.1" -Headers $headers -UseBasicParsing 

$coverage.value.modules | ConvertTo-Json -Depth 10

Output is something like this.

[
    {
        "name":  "clearmeasure.bootcamp.core.dll",
        "signature":  "de8ee6e3-29b6-0446-8cf1-0370d457a7b2",
        "signatureAge":  1,
        "statistics":  {
                           "blocksCovered":  407,
                           "blocksNotCovered":  146,
                           "linesCovered":  241,
                           "linesNotCovered":  86,
                           "linesPartiallyCovered":  11
                       },
        "functions":  [

                      ],
        "fileUrl":  ""
    },
    {
        "name":  "clearmeasure.bootcamp.dataaccess.dll",
        "signature":  "20a6744b-6351-cd43-a8c8-44173f100580",
        "signatureAge":  1,
        "statistics":  {
                           "blocksCovered":  507,
                           "linesCovered":  137
                       },
        "functions":  [

                      ],
        "fileUrl":  ""
    },
...

Including code coverage in your CI build is relatively easy, now getting to 100% is another story.

References