Do I Stub or Shim a method inside my test method?

Question

I have a method base.ResolveDate() inside my test method that's coming from a base class and its public and virtual. I want to stub/shim this method with my own, so do I stub or shim? Stub or Shim, how would I go about doing it? From my experience with MS Fakes it seems like it would be a Stub because Stub can only influence overridable methods. - ALM 2012

Here is the test method:

public override DateTime ResolveDate(ISeries comparisonSeries, DateTime targetDate)
    {
        if (comparisonSeries == null)
        {
            throw new ArgumentNullException("comparisonSeries");
        }

        switch (comparisonSeries.Key)
        {               
            case SeriesKey.SomeKey1:
            case SeriesKey.SomeKey2:
            case SeriesKey.SomeKey3:
            case SeriesKey.SomeKey4:
            case SeriesKey.SomeKey5:
                return DateHelper.PreviousOrCurrentQuarterEnd(targetDate);
        }

        return base.ResolveDate(comparisonSeries, targetDate);
    }

Here is the method from the base class I want to Stub/Shim?

public virtual DateTime ResolveDate(ISeries comparisonSeries, DateTime targetDate)
    {            
        if (this.key == comparisonSeries.Key)
            return targetDate;

        return DateHelper.FindNearestDate(targetDate, comparisonSeries.AsOfDates);
    }

Answer 1

To test a derived method in isolation from its base implementation, you need to shim it. Given the following system under test:

namespace ClassLibrary7
{
    public class Parent
    {
        public virtual string Method()
        {
            return "Parent";
        }
    }

    public class Child : Parent
    {
        public override string Method()
        {
            return base.Method() + "Child";
        } 
    }
}

You can write the following test for the Child.Method().

using ClassLibrary7;
using ClassLibrary7.Fakes;
using Microsoft.QualityTools.Testing.Fakes;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace Test
{
    [TestClass]
    public class UnitTest1
    {
        [TestMethod]
        public void TestMethod1()
        {
            using (ShimsContext.Create())
            {
                var child = new Child();

                var shim = new ShimParent(child);
                shim.Method = () => "Detour";

                string result = child.Method();

                Assert.IsFalse(result.Contains("Parent"));
                Assert.IsTrue(result.Contains("Detour"));
                Assert.IsTrue(result.Contains("Child"));
            }
        }
    }
}

Note that the first two Asserts are included only to illustrate how the parent method is detoured. In a real test only asserts for the child method would be needed.