What is the difference between TypeOf and InstanceOf in NUnit?

Question

In NUnit , what is the difference between Is.TypeOf and Is.InstanceOf ?

In the following example, I've notice that they are both return true:

public class Foo
{
    public Boo GetBoo()
    {
        return new Boo();
    }
}

public class Boo { }

And the NUnit test method:

[Test]
public void GetBoo_WhenCalled_ReturnBoo
{
    var foo = new Foo();
    var result = foo.GetBoo();

    Assert.That(result, Is.TypeOf<Boo>()); //return true
    Assert.That(result, Is.InstanceOf<Boo>()); //return true
}

Answer 1

The documentation is kind of difficult to understand:

TypoOf - tests that an object is an exact Type.

InstanceOf - tests that an obect is an instance of a Type

It means that in contrast to TypoOf , InstanceOf will test also for derivites.

So, in the following example:

public class Foo
{
    public Boo GetBoo()
    {
        return new Woo();
    }
}

public class Woo : Boo { }

Test method:

[Test]
public void GetBoo_WhenCalled_ReturnBoo()
{
    var foo = new Foo();
    var result = foo.GetBoo();

    Assert.that(result, Is.TypeOf<Boo>()); // False ("Boo") 
    Assert.that(result, Is.InstanceOf<Boo>()); //True ("Boo" or "Woo")
}

TypeOf will return false cause it check if the result type is Boo only. InstanceOf will return true cause it check if the result type is Boo or Woo .