Runs OpenCover and ReportGenerator on a dotnet core test project

Measure-Coverage.ps1

[CmdletBinding()]
param(
    [Parameter(ValueFromPipeline)]
    [ValidateScript({Test-Path -Path $_})]
    $ProjectToMeasure  = $PWD, # Allows to pipe in project directiories 

    [Parameter()]
    [switch]$ShowResult
)
begin {
    
    # Solution root is the directory containing a global.json  
    # If it isn't found break execution with an exception

    function Get-AncestorWithGlobalJson {
        $current = Get-Item -Path $ProjectToMeasure
        while($current -and !(Test-Path -Path (Join-Path -Path $current -ChildPath global.json))) {
            $current = Split-Path -Path $current -Parent
        }
        if(!($current)) {
            throw "Couldn't find global.json ascending from directory $ProjectToMeasure"
        }
        return $current
    }
    
    $solutionRoot = Get-AncestorWithGlobalJson

    # coverage information is stored in solutions root .coverage.
    # the directory is created if necessary

    if(Test-Path -Path (Join-Path -Path $PSScriptRoot -ChildPath .coverage)) {
        $script:coverageResultsDirectory = Get-Item -Path (Join-Path -Path $solutionRoot -ChildPath .coverage)
    } else {   
        $script:coverageResultsDirectory = New-Item -Path (join-Path -Path $solutionRoot -ChildPath .coverage) -ItemType Directory
    }

    # I need Nuget.exe

    $script:nuget = (Get-Command nuget.exe).Path

    # Get latest Opencover as nuget package

    & $script:nuget install OpenCover -Output $script:coverageResultsDirectory
    
    # Get hold on the OpenCover executable
    # This might fails if multiple versions of OpenCover are installed. I'll fix it if it happens 

    $script:openCoverConsole = Get-ChildItem -Path $script:coverageResultsDirectory -Filter OpenCover.Console.Exe -Recurse | Select-Object -ExpandProperty FullName

    # Get latest ReportGenerator as a nuget package

    & $script:nuget install ReportGenerator -Output $script:coverageResultsDirectory

    # Get hold on ReportGenerator executable

    $script:reportGenerator = Get-ChildItem -Path $script:coverageResultsDirectory -Filter ReportGenerator.Exe -Recurse | Select-Object -ExpandProperty FullName

    # I need dotnet.exe to execute the tests

    $script:dotnet = (Get-Command dotnet.exe).Path
}
process {

    # I suppose the script is called from within a test project or in the test folder

    $ProjectToMeasure | Get-ChildItem -Filter project.json -Recurse -File | ForEach-Object {
            
        # run all of the found test projects and with dotnet test

        $thisProjectDirectory = $_.Directory
        $thisProjectNamespace = $_.Directory.BaseName
        $thisProjectCoverageOutputFile = (Join-Path -Path $script:coverageResultsDirectory -ChildPath "$thisProjectNamespace.xml")
        
        # call opencover.
        # Let it run dotnet test and write the results to an XML file with the name of the project/assembly.
            
        & $script:openCoverConsole -oldStyle -target:$script:dotnet -targetargs:test -targetdir:$($thisProjectDirectory.FullName) -register:user -output:$thisProjectCoverageOutputFile
    }
}
end {

    # If wanted, show the coverage result

    if($ShowResult.IsPresent) {
    
        # Generate a report for every coverage file found
        & $script:reportGenerator -targetdir:$script:coverageResultsDirectory -reports:([string]::Join(";",(Get-ChildItem -Path $script:coverageResultsDirectory -Filter *.xml | Select-Object -ExpandProperty FullName)))

        # Start default browser with index.html from coverage result directory
        Invoke-Item -Path (Join-Path -Path $script:coverageResultsDirectory -ChildPath index.htm)
    }
}