How do you unit test an interface?

Question

For example, there is a interface IMyInterface, and three classes support this interface:

class A : IMyInterface
{
}

class B : IMyInterface
{
}         


        

Answer 1

If you're using NUnit, then you could use Grensesnitt:

public interface ICanAdd {
    int Add(int i, int j); //dont ask me why you want different adders
}

public class winefoo : ICanAdd {
    public int Add(int i, int j)
    {
        return i + j;
    }
}

interface winebar : ICanAdd {
    void FooBar() ; 
}

public class Adder1 : winebar {
    public int Add(int i, int j) {
        return i + j;
    } 
    public void FooBar() {}
}

public class Adder2 : ICanAdd {
    public int Add(int i, int j) {
        return (i + 12) + (j - 12 ); //yeeeeeaaaah
    } 
}

[InterfaceSpecification]
public class WithOtherPlugins : AppliesToAll
{ 
    [TestCase(1, 2, 3)] 
    [TestCase(-1, 2, 1)]
    [TestCase(0, 0, 0)]
    public void CanAddOrSomething(int x, int y, int r)
    {
        Assert.AreEqual(subject.Add(x, y), r);
    }

    [TestCase(1, 2, Result = 3)]
    [TestCase(-1, 2, Result = 1)]
    [TestCase(0, 0, Result = 0)]
    public int CannAddOrSomethingWithReturn(int x, int y) {
        return subject.Add(x, y);
    }
}