How to write a test case for abstract class method

Question

Here is my code, I want to write a unit test for Build method as part of writing a test case for class D.

public class X
{

}

public interface IB
{
    X GetX(X value);
}

public class B : IB
{
    public X GetX(X value)
    {
        //ToDo:
    }
}

public abstract class A
{
    private IB obj;
    public A(IB obj)
    {
        this.obj = obj;
    }
    public X Build()
    {
        return obj.GetX();
    }
}

public class D : A
{
    public void display()
    {
        //TODO
    }
}

//Test Method

[Test]

public void Test_Build(){
var mock = new Mock<IB>();

var objA = new D();
objA.Build();

}

here is my test method. While calling build method my code is throwing an exception because of not passing the instance of IB. I not sure how to pass a mock object of IB to abstract class A through child class D.

Your code won't compile. `D` can't inherit `A` because the constructors don't match, `public A(IB obj)`. So solve this problem first, then it should become clear. — Liam, Oct 17 '18 at 12:53
Did you see this two thread? https://stackoverflow.com/questions/3604721/how-to-test-a-method-in-an-abstract-class-with-abstract-methods and https://stackoverflow.com/questions/20591869/using-moq-to-test-an-abstract-class — Niraj Trivedi, Oct 17 '18 at 13:00
What have you tried so far? This is kind of "gimme teh codez" as written. — EJoshuaS - Stand with Ukraine, Oct 17 '18 at 13:01
Please try to understand my problem, I want to write a unit test case for the Build method. — Ravikumar, Oct 17 '18 at 13:10
@Ravikumar firstly your code won't compile, Build() doesn't return anything even though it is marked too. — Dave, Oct 17 '18 at 13:12
"I want to write the unit test case for build Method" There is no "the test". It´s up to you what you need to test. You can write dozens of unit-tests for a single method, depending on what that method does. How should we know what your method is supposed to do and therefor how a test for that method should look like? — MakePeaceGreatAgain, Oct 17 '18 at 13:19

score 3 · Accepted Answer · answered Oct 17 '18 at 13:47

This is because Constructors are not inherited in C#.

Your base class, A has a constructor that takes an instance of IB and intialises the field. However your inheriting class has no constructor specified and so has a Default parameterless constructor.

You need to provide a constructor for D that takes an instance of IB and then pass this upto the base constructor like this

public D(IB instanceOfIB)
    : base(instanceofIB)
{
    //do other things here if you want or leave empty
}

@Ravikumar Here is a good article by Jon Skeet on Constructors. They are not as simple as they seem. http://jonskeet.uk/csharp/constructors.html — Dave, Oct 17 '18 at 13:55

How to write a test case for abstract class method

1 Answers1