Generic Method to Clear a Class and Intelli-Test

March 18, 2016

Recently, I published this article on copying a class dynamically. I then found that I could use the same approach to clear a class. Here’s the method:



        private static void ClearClass<T>(T classToClear)
        {
            if (classToClear == null)
                throw new Exception("Must not specify null parameters");

            var properties = classToClear.GetType().GetProperties();

            foreach (var p in properties.Where(prop => prop.CanWrite))
            {
                p.SetValue(classToClear, GetDefault(p.PropertyType));
            }
        }

        /// <summary>
        /// Taken from http://stackoverflow.com/questions/474841/dynamically-getting-default-of-a-parameter-type
        /// </summary>
        /// <param name="type"></param>
        /// <returns></returns>
        public static object GetDefault(Type type)
        {
            return type.IsValueType ? Activator.CreateInstance(type) : null;
        }

As you can see, I had a little help from Jon Skeet with this one. Once I’d written it, I thought I’d have a play with the IntelliTest feature: if you right click the method and select “Create IntelliTest”, you’re presented with this:

It generated this:




    /// <summary>This class contains parameterized unit tests for Program</summary>
    [PexClass(typeof(Program))]
    [PexAllowedExceptionFromTypeUnderTest(typeof(InvalidOperationException))]
    [PexAllowedExceptionFromTypeUnderTest(typeof(ArgumentException), AcceptExceptionSubtypes = true)]
    [TestClass]
    public partial class ProgramTest
    {
        /// <summary>Test stub for ClearClass(!!0)</summary>
        [PexGenericArguments(typeof(int))]
        [PexMethod]
        internal void ClearClassTest<T>(T classToClear)
        {
            Program.ClearClass<T>(classToClear);
            // TODO: add assertions to method ProgramTest.ClearClassTest(!!0)
        }
    }

The interesting thing about this, is that it can’t be found as a test. What actually happens is this creates an intelli-test, which, as far as I can see, you have to right-click on the created test and select “Run Intelli-test”. This then creates you an actual unit test:

It looks something like this:




namespace ConsoleApplication13.Tests
{
    public partial class ProgramTest
    {

[TestMethod]
[PexGeneratedBy(typeof(ProgramTest))]
public void ClearClassTest861()
{
    this.ClearClassTest<int>(0);
}
    }
}

That then can be found and run:

Obviously, looking at the unit test, it’s not a particularly good one; it effectively tests that your code doesn’t crash, so it increases your code coverage, but doesn’t really test anything per-se.