xUnit Tests Not Running With .NET Standard

Having worked with C# for quite some time now writing desktop applications, I’ve begun making the transition over to .NET standard. In my professional working experience, it was a much slower transition because of product requirements and time, but in my own personal development there’s no reason why I couldn’t get started with it. And call me crazy, but I enjoy writing coded tests for the things I make. My favourite testing framework for my C# development is xUnit, and naturally as I started writing some new code with .NET Standard I wanted to make sure I could get my tests to run.

Here’s an example of some C# code I wrote for my unit tests of a simple LRU cache class I was playing around with:

    [ExcludeFromCodeCoverage]
    public sealed class LruCachetests
    {
        [Fact]
        public void Constructor_CapacityTooSmall_ThrowsArgumentException()
        {
            Assert.Throws<ArgumentException>(() => new LruCache<int, int>(0));
        }

        [Fact]
        public void ContainsKey_EntryExists_True()
        {
            var cache = new LruCache<int, int>(1);
            cache.Add(0, 1);
            var actual = cache.ContainsKey(0);
            Assert.True(
                actual,
                $"Unexpected result for '{nameof(LruCache<int, int>.ContainsKey)}'.");
        }
    }

Pretty simple stuff. I know that for xUnit in Visual Studio, I need to get a nuget package for the test runner to work right in the IDE. Simple enough, I just need to add the “xunit.runner.visualstudio” package alongside the xunit package I had already included into my test project.

Nuget package management for project in visual studio showing required xUnit packages.
Required xUnit nuget packages

Ready to rock! So I go run all my tests in the solution but I’m met with this little surprise:

[3/24/2020 3:59:10.570 PM] ========== Discovery aborted: 0 tests found (0:00:00.0622045) ==========
[3/24/2020 3:59:20.510 PM] ---------- Discovery started ----------
Microsoft.VisualStudio.TestPlatform.ObjectModel.TestPlatformException: Unable to find C:[redacted]binDebugnetstandard2.0testhost.dll. Please publish your test project and retry.
   at Microsoft.VisualStudio.TestPlatform.CrossPlatEngine.Hosting.DotnetTestHostManager.GetTestHostPath(String runtimeConfigDevPath, String depsFilePath, String sourceDirectory)
   at Microsoft.VisualStudio.TestPlatform.CrossPlatEngine.Hosting.DotnetTestHostManager.GetTestHostProcessStartInfo(IEnumerable`1 sources, IDictionary`2 environmentVariables, TestRunnerConnectionInfo connectionInfo)
   at Microsoft.VisualStudio.TestPlatform.CrossPlatEngine.Client.ProxyOperationManager.SetupChannel(IEnumerable`1 sources, String runSettings)
   at Microsoft.VisualStudio.TestPlatform.CrossPlatEngine.Client.ProxyDiscoveryManager.DiscoverTests(DiscoveryCriteria discoveryCriteria, ITestDiscoveryEventsHandler2 eventHandler)
[3/24/2020 3:59:20.570 PM] ========== Discovery aborted: 0 tests found (0:00:00.0600179) ==========
Executing all tests in project: [redacted].Tests
[3/24/2020 3:59:20.635 PM] ---------- Run started ----------
[3/24/2020 3:59:20.639 PM] ========== Run finished: 0 tests run (0:00:00.0039314) ==========

Please publish your test project and retry? Huh?

As any software engineer does, I set out to Google for answers. I came across this Stack Overflow post: https://stackoverflow.com/q/54770830/2704424

And fortunately someone had responded with a link to the xUnit documentation: Why doesn’t xUnit.net support netstandard?

The answer was right at the top!

netstandard is an API, not a platform. Due to the way builds and dependency resolution work today, xUnit.net test projects must target a platform (desktop CLR, .NET Core, etc.) and run with a platform-specific runner application.

https://xunit.net/docs/why-no-netstandard

My solution was that I changed my test project to build for one of the latest .NET Frameworks… and voila! I chose .NET 4.8 as the latest available at the time of writing.

My next attempt at running all of my tests looked like this:

Executing all tests in project: [Redacted].Tests
[3/24/2020 3:59:20.635 PM] ---------- Run started ----------
[3/24/2020 3:59:20.639 PM] ========== Run finished: 0 tests run (0:00:00.0039314) ==========
[3/24/2020 4:08:14.898 PM] ---------- Discovery started ----------
[xUnit.net 00:00:00.00] xUnit.net VSTest Adapter v2.4.1 (32-bit Desktop .NET 4.0.30319.42000)
[xUnit.net 00:00:00.40]   Discovering: [Redacted].Tests
[xUnit.net 00:00:00.47]   Discovered:  [Redacted].Tests
[xUnit.net 00:00:00.00] xUnit.net VSTest Adapter v2.4.1 (32-bit Universal Windows)
[3/24/2020 4:08:16.289 PM] ========== Discovery finished: 2 tests found (0:00:01.3819229) ==========
Executing all tests in project: [Redacted].Tests
[3/24/2020 4:08:17.833 PM] ---------- Run started ----------
[xUnit.net 00:00:00.00] xUnit.net VSTest Adapter v2.4.1 (32-bit Desktop .NET 4.0.30319.42000)
[xUnit.net 00:00:00.41]   Starting:    [Redacted].Tests
[xUnit.net 00:00:00.66]   Finished:    [Redacted].Tests
[3/24/2020 4:08:19.337 PM] ========== Run finished: 2 tests run (0:00:01.4923808) ==========

And I was back on my path to success! Hopefully if you run into this same issue you can resolve it in the same fashion. Happy testing!

Nick Cosentino

Principal Software Engineering Manager at Microsoft. Views are my own.

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