Why is a ClassInitialize decorated method making all my tests fail?

Question

I understand, from MSDN, that ClassInitialize is to mark a method that will do setup code for all tests, once, before all tests run. When I include such a method in the abridged fixture below, all tests fail. As soon as I comment it out, they pass again.

[TestClass]
public class AuthenticationTests
{
    [ClassInitialize]
    public void SetupAuth()
    {
        var x = 0;
    }

    [TestMethod]
    public void TestRegisterMemberInit()
    {
        Assert.IsTrue(true);
    }
}

Answer 1

The [ClassInitialize] decorated method should be static and take exactly one parameter of type TestContext:

[ClassInitialize]
public static void SetupAuth(TestContext context)
{
    var x = 0;
}

In fact, if I copy-paste your code into a clean VS project, the testrunner explains exactly that in the error message:

Method UnitTestProject1.AuthenticationTests.SetupAuth has wrong signature. The method must be static, public, does not return a value and should take a single parameter of type TestContext.

Answer 2

Method marked with [ClassInitialize]:

1. Apply to only one method of a test class.
2. The class must be sealed, i.e. not inherited.
3. The method has to be public static.
4. The method must pass a TestContext parameter.
5. The Method does not return a value.

Answer 3

In VS2015, the failure to have the TestContext parameter causes this most unhelpful error to be output when you run the test (in case anyone is searching on the exception, like I was):

Exception thrown: 'Microsoft.VisualStudio.TestPlatform.MSTestFramework.TypeInspectionException' in Microsoft.VisualStudio.TestPlatform.Extensions.VSTestIntegration.dll