Determine if code is running as part of a unit test

I have a unit test (nUnit). Many layers down the call stack a method will fail if it is running via a unit test.

Ideally you would use something like mocking to setup the object that this method is depending on but this is 3rd party code and I can't do that without a lot of work.

I don't want setup nUnit specific methods - there are too many levels here and its a poor way of doing unit test.

Instead what I would like to do is to add something like this deep down in the call stack

#IF DEBUG // Unit tests only included in debug build
if (IsRunningInUnitTest)
   {
   // Do some setup to avoid error
   }
#endif

So any ideas about how to write IsRunningInUnitTest?

P.S. I am fully aware that this is not great design, but I think its better than the alternatives.

I've done this before - I had to hold my nose while I did it, but I did it. Pragmatism beats dogmatism every time. Of course, if there is a nice way you can refactor to avoid it, that would be great.

Basically I had a "UnitTestDetector" class which checked whether the NUnit framework assembly was loaded in the current AppDomain. It only needed to do this once, then cache the result. Ugly, but simple and effective.

Taking Jon's idea this is what I came up with -

using System;
using System.Reflection;

/// <summary>
/// Detect if we are running as part of a nUnit unit test.
/// This is DIRTY and should only be used if absolutely necessary 
/// as its usually a sign of bad design.
/// </summary>    
static class UnitTestDetector
{

    private static bool _runningFromNUnit = false;      

    static UnitTestDetector()
    {
        foreach (Assembly assem in AppDomain.CurrentDomain.GetAssemblies())
        {
            // Can't do something like this as it will load the nUnit assembly
            // if (assem == typeof(NUnit.Framework.Assert))

            if (assem.FullName.ToLowerInvariant().StartsWith("nunit.framework"))
            {
                _runningFromNUnit = true;
                break;
            }
        }
    }

    public static bool IsRunningFromNUnit
    {
        get { return _runningFromNUnit; }
    }
}

Pipe down at the back we're all big enough boys to recognise when we're doing something we probably shouldn't ;)

Adapted from Ryan's answer. This one is for the MS unit test framework.

The reason I need this is because I show a MessageBox on errors. But my unit tests also test the error handling code, and I don't want a MessageBox to pop up when running unit tests.

/// <summary>
/// Detects if we are running inside a unit test.
/// </summary>
public static class UnitTestDetector
{
    static UnitTestDetector()
    {
        string testAssemblyName = "Microsoft.VisualStudio.QualityTools.UnitTestFramework";
        UnitTestDetector.IsInUnitTest = AppDomain.CurrentDomain.GetAssemblies()
            .Any(a => a.FullName.StartsWith(testAssemblyName));
    }

    public static bool IsInUnitTest { get; private set; }
}

And here's a unit test for it:

    [TestMethod]
    public void IsInUnitTest()
    {
        Assert.IsTrue(UnitTestDetector.IsInUnitTest, 
            "Should detect that we are running inside a unit test."); // lol
    }

Simplifying Ryan's solution, you can just add the following static property to any class:

	public static readonly bool IsRunningFromNUnit = 
		AppDomain.CurrentDomain.GetAssemblies().Any(
            a => a.FullName.ToLowerInvariant().StartsWith("nunit.framework"));

I use a similar approach as tallseth

This is the basic code which could be easily modified to include caching. Another good idea would be to add a setter to IsRunningInUnitTest and call UnitTestDetector.IsRunningInUnitTest = false to your projects main entry point to avoid the code execution.

public static class UnitTestDetector
{
    public static readonly HashSet<string> UnitTestAttributes = new HashSet<string> 
    {
        "Microsoft.VisualStudio.TestTools.UnitTesting.TestClassAttribute",
        "NUnit.Framework.TestFixtureAttribute",
    };
    public static bool IsRunningInUnitTest
    {
        get
        {
            foreach (var f in new StackTrace().GetFrames())
                if (f.GetMethod().DeclaringType.GetCustomAttributes(false).Any(x => UnitTestAttributes.Contains(x.GetType().FullName)))
                    return true;
            return false;
        }
    }
}

Maybe useful, checking current ProcessName:

public static bool UnitTestMode
{
    get 
    { 
        string processName = System.Diagnostics.Process.GetCurrentProcess().ProcessName;

        return processName == "VSTestHost"
                || processName.StartsWith("vstest.executionengine") //it can be vstest.executionengine.x86 or vstest.executionengine.x86.clr20
                || processName.StartsWith("QTAgent");   //QTAgent32 or QTAgent32_35
    }
}

And this function should be also check by unittest:

[TestClass]
public class TestUnittestRunning
{
    [TestMethod]
    public void UnitTestRunningTest()
    {
        Assert.IsTrue(MyTools.UnitTestMode);
    }
}

References:
Matthew Watson in http://social.msdn.microsoft.com/Forums/en-US/csharplanguage/thread/11e68468-c95e-4c43-b02b-7045a52b407e/

In test mode, Assembly.GetEntryAssembly() seems to be null.

#IF DEBUG // Unit tests only included in debug build 
  if (Assembly.GetEntryAssembly() == null)    
  {
    // Do some setup to avoid error    
  }
#endif 

Note that if Assembly.GetEntryAssembly() is null, Assembly.GetExecutingAssembly() isn't.

The documentation says: The GetEntryAssembly method can return null when a managed assembly has been loaded from an unmanaged application.

Somewhere in the project being tested:

public static class Startup
{
    public static bool IsRunningInUnitTest { get; set; }
}

Somewhere in your unit test project:

[TestClass]
public static class AssemblyInitializer
{
	[AssemblyInitialize]
	public static void Initialize(TestContext context)
	{
		Startup.IsRunningInUnitTest = true;
	}
}

Elegant, no. But straightforward and fast. AssemblyInitializer is for MS Test. I would expect other test frameworks to have equivalents.

Just use this:

AppDomain.CurrentDomain.IsDefaultAppDomain()

In test mode, it will return false.

I use this only for skipping logic that disables all TraceAppenders in log4net during startup when no debugger is attached. This allows unit tests to log to the Resharper results window even when running in non-debug mode.

The method that uses this function is either called on startup of the application or when beginning a test fixture.

It is similar to Ryan's post but uses LINQ, drops the System.Reflection requirement, does not cache the result, and is private to prevent (accidental) misuse.

    private static bool IsNUnitRunning()
    {
        return AppDomain.CurrentDomain.GetAssemblies().Any(assembly => assembly.FullName.ToLowerInvariant().StartsWith("nunit.framework"));
    }

Having a reference to nunit framework doesn't mean that test is actually running. For example in Unity when you activate play mode tests the nunit references are added to the project. And when you run a game the references are exist, so UnitTestDetector would not work correctly.

Instead of checking for nunit assembly we can ask nunit api to check is code under executing test now or not.

using NUnit.Framework;

// ...

if (TestContext.CurrentContext != null)
{
    // nunit test detected
    // Do some setup to avoid error
}

Edit:

Beware that the TestContext may be automatically generated if it's required.

works like a charm

if (AppDomain.CurrentDomain.GetAssemblies().FirstOrDefault(x => x.FullName.ToLowerInvariant().StartsWith("nunit.framework")) != null)
{
    fileName = @"C:\Users\blabla\xxx.txt";
}
else
{
    var sfd = new SaveFileDialog
    {     ...     };
    var dialogResult = sfd.ShowDialog();
    if (dialogResult != DialogResult.OK)
        return;
    fileName = sfd.FileName;
}

.

Unit tests will skip application entry point. At least for wpf, winforms and console application main() is not being called.

If main method is called than we are in run-time, otherwise we are in unit test mode:

public static bool IsUnitTest { get; private set; } = true;

[STAThread]
public static void main()
{
    IsUnitTest = false;
    ...
}

I have a solution that's closer to what the original poster wanted. The issue is how to set the test flag to indicate the code is executing as part of a test. This can be implemented with 2 lines of code.

I have added an internal variable called RunningNunitTest at the top of the class. Be sure to make this an internal variable and not public. We don't want to export this variable when we build the project. Also this is how we're going to allow NUnit to set it to true.

NUnit does not have access to private variables or methods in our code. This is an easy fix. In between the using statements and the namespace add a [assembly: InternalsVisibleTo("NUnitTest")] decoration. This allows NUint access to any internal variable or method. My NUnit test project is named "NUintTest." Replace this name with the name of your NUint test Project.

That's it! Set RunningNunitTest to true in your NUnit tests.

using NetworkDeviceScanner;

[assembly: InternalsVisibleTo("NUnitTest")] // Add this decoration to your class

namespace NetworkDeviceScannerLibrary
{
    public class DetectDevice
    {
        internal bool RunningNunitTest = false; // Add this variable to your class

        public ulong TotalAddressesFound;
        public ulong ScanCount;

NUnit Code

var startIp = IPAddress.Parse("191.168.1.1");
var endIp = IPAddress.Parse("192.168.1.128");
var detectDevice = new DetectDevice
{
    RunningNunitTest = true
};
Assert.Throws<ArgumentOutOfRangeException>(() => detectDevice.DetectIpRange(startIp, endIp, null));

I was unhappy to have this problem recently. I solved it in a slightly different way. First, I was unwilling to make the assumption that nunit framework would never be loaded outside a test environment; I was particularly worried about developers running the app on their machines. So I walked the call stack instead. Second, I was able to make the assumption that test code would never be run against release binaries, so I made sure this code did not exist in a release system.

internal abstract class TestModeDetector
{
    internal abstract bool RunningInUnitTest();

    internal static TestModeDetector GetInstance()
    {
    #if DEBUG
        return new DebugImplementation();
    #else
        return new ReleaseImplementation();
    #endif
    }

    private class ReleaseImplementation : TestModeDetector
    {
        internal override bool RunningInUnitTest()
        {
            return false;
        }
    }

    private class DebugImplementation : TestModeDetector
    {
        private Mode mode_;

        internal override bool RunningInUnitTest()
        {
            if (mode_ == Mode.Unknown)
            {
                mode_ = DetectMode();
            }

            return mode_ == Mode.Test;
        }

        private Mode DetectMode()
        {
            return HasUnitTestInStack(new StackTrace()) ? Mode.Test : Mode.Regular;
        }

        private static bool HasUnitTestInStack(StackTrace callStack)
        {
            return GetStackFrames(callStack).SelectMany(stackFrame => stackFrame.GetMethod().GetCustomAttributes(false)).Any(NunitAttribute);
        }

        private static IEnumerable<StackFrame> GetStackFrames(StackTrace callStack)
        {
            return callStack.GetFrames() ?? new StackFrame[0];
        }

        private static bool NunitAttribute(object attr)
        {
            var type = attr.GetType();
            if (type.FullName != null)
            {
                return type.FullName.StartsWith("nunit.framework", StringComparison.OrdinalIgnoreCase);
            }
            return false;
        }

        private enum Mode
        {
            Unknown,
            Test,
            Regular
        }

Application.Current is null when running under the unit tester. At least for my WPF app using MS Unit tester. That's an easy test to make if needed. Also, something to keep in mind when using Application.Current in your code.

            if (string.IsNullOrEmpty(System.Web.Hosting.HostingEnvironment.MapPath("~")))
            {
                // Running not as a web app (unit tests)
            }

            // Running as a web app

Considering your code is normaly run in the main (gui) thread of an windows forms application and you want it to behave different while running in a test you can check for

if (SynchronizationContext.Current == null)
{
    // code running in a background thread or from within a unit test
    DoSomething();
}
else
{
    // code running in the main thread or any other thread where
    // a SynchronizationContext has been set with
    // SynchronizationContext.SetSynchronizationContext(synchronizationContext);
    DoSomethingAsync();
}

I am using this for code that I want to fire and forgot in a gui application but in the unit tests I might need the computed result for an assertation and I don't want to mess with multiple threads running.

Works for MSTest. The advantage it that my code does not need to check for the testing framework itself and if I really need the async behaviour in a certain test I can set my own SynchronizationContext.

Be aware that this is not a reliable method to Determine if code is running as part of a unit test as requested by OP since code could be running inside a thread but for certain scenarios this could be a good solution (also: If I am already running from a background thread, it might not be necessary to start a new one).

I've used the following in VB in my code to check if we ae in a unit test. spifically i didn't want the test to open Word

    If Not Application.ProductName.ToLower().Contains("test") then
        ' Do something 
    End If

How about using reflection and something like this:

var underTest = Assembly.GetCallingAssembly() != typeof(MainForm).Assembly;

The calling assembly will be where your test cases are and just substitute for MainForm some type that's in your code being tested.

There is a really simple solution as well when you are testing a class...

Simply give the class you are testing a property like this:

// For testing purposes to avoid running certain code in unit tests.
public bool thisIsUnitTest { get; set; }

Now your unit test can set the "thisIsUnitTest" boolean to true, so in the code you want to skip, add:

   if (thisIsUnitTest)
   {
       return;
   } 

Its easier and faster than inspecting the assemblies. Reminds me of Ruby On Rails where you'd look to see if you are in the TEST environment.