Easy Steps for 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 favorite 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. But I did hit a little snag with my xUnit tests not running... Let's check it out!

xUnit Tests - The Example

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.

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

The Solution To My xUnit Troubles

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!