Question

This “question” is a documentation of an odd MSTest behaviour I’ve banged my head against a few times, in the hope that it will be useful to other people that encounter the same problem. Consider the following test:

[TestClass]
public class SomeTest {
    private List<int> _list;

    [TestInitialize]
    public void SetUp() {
        DoSomething();
        _list = new List<int>();
    }

    [TestMethod]
    public void SomeTestMethod() {
        _list.Add(42);
        ...
    }
}

Running it produces a System.NullReferenceException: Object reference not set to an instance of an object. on the _list.Add(42); line. It looks like SetUp(), although it has the correct public void signature and the [TestInitialize] attribute, isn’t invoked. What happened?

Answer 1

In this case, further investigation showed that DoSomething() was throwing an exception. For reasons I cannot comprehend, MSTest (at least when invoked from Visual Studio with ReSharper) swallows exceptions thrown by the [TestInitialize] method and continues with the test method anyway without failing the test.

(If anyone can explain the rationale for this behaviour or how it can be turned off, I’d be grateful.)