Simple `Assert.IsAssignableFrom <T>` crash

Question

Why does this simple statement statement fail? From what I read, it should be. Unfortunately, since the functionality is so basic, there is not much information.

public interface IDummy{} public class Dummy : IDummy {} Assert.IsAssignableFrom<IDummy>(new Dummy()); 

Performing this test gives

 Expected: assignable from <Application.Tests.ViewModels.IDummy> But was: <Application.Tests.ViewModels.Dummy> 

I tried to replace the interface and some of the objects to no avail.

Answer 1

IsAssignableFrom works in the opposite direction from what you expect. He asks: Is (value) Assignable From IDummy. Or: "Assigned (value)?"

From an XML document: /// Claims that an object can be assigned a value of this type.

You probably need Assert.IsInstanceOfType ()

Answer 2

In the interest of those who land here via Google (or Bing :-))

Assert.IsAssignableFrom<T>(object actual) intended to check whether the test object can be replaced by type T. Effectively this means that this statement checks the "is-a" relationship between the object and type T.

Let's look at some code (intentionally simplified):

 // The Base class public class Employee { public int EmployeeId { get; set; } public string FirstName { get; set; } public string LastName { get; set; } public DateTime DateOfJoining { get; set; } } // The derived class public class Manager : Employee { public IList<Employee> EmployeesReporting { get; set; } } 

Now the statement:

 // NOTE: using Assert = NUnit.Framework.Assert; [TestMethod] public void Test_IsAssignableFrom() { var employee = new Employee(); // Manager is-a Employee, so the below is true Assert.IsAssignableFrom<Manager>(employee); } 

While IsInstanceOf<T>(object actual) intended to check whether the test object (for example, the name) is an instance of type T - just put it if the "actual" is a type T or a type derived from T

 [TestMethod] public void Test_IsAssignableFrom() { var manager = new Manager(); // Manager derives from Employee so the below is true Assert.IsInstanceOf<Employee>(manager); } 

EDIT It turns out that these statements work the same as the Type.IsAssignableFrom and Type.IsInstanceOf methods on System.Type