How to diagnose "TestFixtureSetUp Failed"

If you are using SpecFlow and C# in Visual Studio, look at the auto-generated <whatever>.feature.cs file after the test fails. On the public partial class <whatever>Feature line, you should see a symbol which when hovered over will show the reason that the NUnit fixture setup failed. In my case, it was that some of my BeforeFeature methods in my TestHooks class were not static. All BeforeTestRun, AfterTestRun, BeforeFeature, and AfterFeature methods need to be static.

I had this symptom caused by an error during field initialization. If you initialize your fields in the [SetUp] method, you should see a better error message.

[TestFixture]
internal class CommandParserTest
{
    // obscure error message
    private CommandParser parser = new CommandParser(...);
    ...
}

[TestFixture]
internal class CommandParserTest
{
    private CommandParser parser;

    [SetUp]
    public void BeforeTest()
    {
        // better error message
        parser = new CommandParser(...);
    }
    ...
}