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Concurrent Test Running with Specflow and NUnit 3

A little while back I wrote a post on achieving concurrent or parallel test running with Selenium, Specflow and NUnit2, but what about NUnit3? Let’s have a look at that, thankfully it is a bit simpler than running an external build script as done previously.

First up, according to the Specflow docs – open up your AssemblyInfo.cs file in your project and add the following line:

[assembly: Parallelizable(ParallelScope.Fixtures)]

Next we need to setup/ teardown our browser and config from the Scenario Hook level, doing it in a Test Run Hook will be problematic as it is static. Your Hooks might look similar to this:

public class ScenarioHooks
private readonly IObjectContainer objectContainer;
private IWebDriver Driver;

public ScenarioHooks(IObjectContainer objectContainer)
this.objectContainer = objectContainer;

public void BeforeScenario()
var customCapabilitiesIE = new DesiredCapabilities();
customCapabilitiesIE.SetCapability(CapabilityType.BrowserName, "internet explorer");
customCapabilitiesIE.SetCapability(CapabilityType.Platform, new Platform(PlatformType.Windows));
customCapabilitiesIE.SetCapability("", @"C:\tmp\webdriver\iedriver\iedriver_3.0.0_Win32bit.exe");

Driver = new RemoteWebDriver(new Uri(XXX.XXX.XXX.XXX), customCapabilitiesIE);

public void AfterScenario()

You can see from the browser instantiation we are sending the tests to a Selenium Grid Hub, so as a precursor to running the tests you will need suitable infrastructure to run a grid, or you could configure it to go off to SauceLabs or BrowserStack.

Assuming the hub and nodes are configured correctly, when your build process runs the tests then the hub will farm them out by feature file (for other options see the parallel scope in AssemblyInfo.cs) to achieve concurrent test running, and that’s it! Much nicer.

Gallio Test Runner

Gallio (sometimes known as MB Unit or Gallio Icarus) is a test runner which to me has two distinct advantages over MsTest and NUnit.

Parallel test execution support and built in test reports, although NUnit does have parallel support with PNUnit.

How to set it up

  • Download and install Gallio from here.
  • In your Visual Studio Project navigate to Project > [project name] Properties from the drop down menu.
  • Click Debug
  • Set startup program to Gallio, by default it should be somewhere like: C:\Program Files\Gallio\bin\Gallio.Icarus.exe
  • In Start Options > Command Line Arguments paste in the path of your projects DLL housing the tests you want to execute
  • Save
  • Hit Start when you want to run or debug your tests


Gallio GUI

This looks very similar to NUnit but with some extra buttons and menus, the only ones you will really care about are start/ stop/ debug and test reports.


The reports aren’t anywhere near as nice as that you would find in Allure, but they are easily generated and easy to view.


Bootnote: In Gallio Icarus select menu Tools -> Options, select page “Preferences”, set “Test Runner Factory” to IsolatedAppDomain or Local to get the debugger to work.

Parallel Test Execution with Specflow

Running Specflow scenarios in Parallel is a tricky problem to solve due to the nature of how tests are written. Achieving this is a lot simpler if we write Selenium tests in a unit style fashion but as this isn’t the case for Specflow with its Gherkin syntax we will look at executing them with a powershell build script against a Browserstack grid.

Thanks to this great article from Kenneth Truyers, it has really helped me to achieve this. We will look at executing parallel Specflow tests against a BrowserStack grid.

Set Up

In our Initialisation method we need to specify our remote driver whilst passing in our varying desired capabilities in Config.

private static void SetupCloudDriver()
            var capabilities = new DesiredCapabilities();

            capabilities.SetCapability(CapabilityType.Version, ConfigurationManager.AppSettings["version"]);
            capabilities.SetCapability("os", ConfigurationManager.AppSettings["os"]);
            capabilities.SetCapability("os_version", ConfigurationManager.AppSettings["os_version"]);
            capabilities.SetCapability("browserName", ConfigurationManager.AppSettings["browser"]);

            capabilities.SetCapability("browserstack.user", ConfigurationManager.AppSettings["browserstack.user"]);
            capabilities.SetCapability("browserstack.key", ConfigurationManager.AppSettings["browserstack.key"]);
            capabilities.SetCapability("browserstack.local", false);
            capabilities.SetCapability("browserstack.debug", true);

            capabilities.SetCapability("project", "Project Name");

            Driver = new RemoteWebDriver(new Uri(ConfigurationManager.AppSettings["browserstack.hub"]), capabilities);
            ScenarioContext.Current["driver"] = Driver;

Config for Cross Browser spin up

One of our config files might look like so:

<xml version="1.0" encoding="utf-8">
<configuration xmlns:xdt="">
        <add key="browser" value="Safari" xdt:Transform="Insert"/>
        <add key="os" value="osx" xdt:Transform="Insert"/>
        <add key="version" value="8" xdt:Transform="Insert"/>
        <add key="os_version" value="Yosemite" xdt:Transform="Insert"/>

This tells Browserstack what system to spin up and run the tests against for one parallel instance, multiple config files with other systems are needed so they can all be executed depending on your requirements. Furthermore we need to set these up in Configuration Manager so that each config picks up the tests when the solution is built.

What This Enables

We can select what environment we wish to run against, run the test and see it appear in Browserstack (not in parallel) or run it locally using our own setup.


So now we have essentially got a single test running in the cloud (and our config still allows us to run locally if we choose), next we need to kick off a bunch of these against different systems.

The Build Script

We use a PowerShell build script to achieve the parallel part of this, here it is:

$solution = "Your.Testing.Solution.sln"

function Get-SolutionConfigurations($solution)
        Get-Content $solution |
        Where-Object {$_ -match "(?&lt;config&gt;\w+)\|"} |
        %{ $($Matches['config'])} |
        select -uniq

$frameworkDirs = @((Get-ItemProperty -Path "HKLM:\SOFTWARE\Microsoft\MSBuild\ToolsVersions\12.0" -Name "MSBuildToolsPath32")."MSBuildToolsPath32",
    for ($i = 0; $i -lt $frameworkDirs.Count; $i++) {
        $dir = $frameworkDirs[$i]
        if ($dir -Match "\$\(Registry:HKEY_LOCAL_MACHINE(.*?)@(.*)\)") {
            $key = "HKLM:" + $matches[1]
            $name = $matches[2]
            $dir = (Get-ItemProperty -Path $key -Name $name).$name
            $frameworkDirs[$i] = $dir

    $env:path = ($frameworkDirs -join ";") + ";$env:path"

@(Get-SolutionConfigurations $solution) | foreach {
      Write-Host "Building for $_"
    msbuild $solution /p:Configuration=$_ /nologo /verbosity:quiet
 New-Item "$(get-location)\packages\specflow.1.9.0\tools\specflow.exe.config" -type file -force -value "&lt;?xml version=""1.0"" encoding=""utf-8"" ?&gt; &lt;configuration&gt; &lt;startup&gt; &lt;supportedRuntime version=""v4.0.30319"" /&gt; &lt;/startup&gt; &lt;/configuration&gt;" | Out-Null

@(Get-SolutionConfigurations $solution)| foreach {
    Start-Job -ScriptBlock {
        param($configuration, $basePath)

            &amp; $basePath\packages\NUnit.Runners.2.6.4\tools\nunit-console.exe /labels /out=$basePath\nunit_$configuration.txt /xml:$basePath\nunit_$configuration.xml /nologo /config:$configuration "$basePath/Your.Testing.Solution/bin/$configuration/Your.Testing.Solution.dll"
            &amp; $basePath\packages\specflow.1.9.0\tools\specflow.exe nunitexecutionreport "$basePath\Your.Testing.Solution\Your.Testing.Solution.csproj" /out:$basePath\specresult_$configuration.html /xmlTestResult:$basePath\nunit_$configuration.xml /testOutput:nunit_$configuration.txt

    } -ArgumentList $_, $(get-location)
Get-Job | Wait-Job
Get-Job | Receive-Job

It obviously needs tweaking in areas to point to your solution but what the hell is it actually doing? It is running msbuild against each config file and executing the test suite. Our Safari based config gets built and executed against BrowserStack as do any other configurations. A test report for each config/ system is then generated to let you know the outcome of that particular run.

Running the script should allow you to see parallel test execution against your desired systems in Browserstack:


Generated Feedback and Reporting

Reports generated after look similar to the below:


What Next?

You will undoubtedly encounter issues with Browserstack seeing your internal test environments, this is something that you will need to consider. Consult the Browserstack documentation online regarding tunnelling or running Browserstack locally.

We can also throw in some automated visual checking to really get the ball rolling with Continuous Delivery. If you have some well set up Applitools Eyes base images then visual checking on many systems at once is potentially worth thousands of checks.