Reduce duplication in NUnit tests for different implementations of interface

Question

I have the following interface:

public interface IStack
{
    int Peek();
    void Push(int i);
}

And two implementations:

public class LinkedListStack : IStack
{
    public void Push(int x)
    {
     ...
    }

    public int Peek()
    {
     ...
    }
}

public class ArrayStack : IStack
{
    public void Push(int i)
    {
     ...
    }

    public int Peek()
    {
     ...
    }
}

For my unit tests - I currently have something like this, two files containing the same tests - the only difference being the implementation:

LinkedListStackTest.cs:

public class LinkedListStackTest
{
    [Test]
    public void PushToStack()
    {
        //Arrange
        IStack stack = new LinkedListStack();

        //Act
        stack.Push(1);

        //Assert
        Assert.AreEqual(1, stack.Peek());
    }
}

ArrayStackTest.cs

public class ArrayStackTest
{
    [Test]
    public void PushToStack()
    {
        //Arrange
        IStack stack = new ArrayStack();

        //Act
        stack.Push(1);

        //Assert
        Assert.AreEqual(1, stack.Peek());
    }
}

Given the tests for the implementations should be the same - is there a way I can write a single set of NUnit tests that will run against all my implementations of IStack?

Answer 1

You can use the TestCaseSourceAttribute:

[Test]
[TestCaseSource(typeof(StackTestCases))]
public void PushToStack(IStack stack)
{
    //Arrange/Act
    stack.Push(1);

    //Assert
    Assert.AreEqual(1, stack.Peek());
}

Implementation of StackTestCases:

internal class StackTestCases : IEnumerable
{
    public static IEnumerable TestCases
    {
        get
        {
            yield return new TestCaseData(new LinkedListStack());
            yield return new TestCaseData(new ArrayStack());
        }
    }

    /// <inheritdoc />
    public IEnumerator GetEnumerator()
    {
        return TestCases.GetEnumerator();
    }
}

Please note that the test method will take an IStack as a parameter:

[Test]
[TestCaseSource(typeof(StackTestCases))]
public void PushToStack(IStack stack)

...And you can return the different implementations of IStack in TestCases property of StackTestCases:

yield return new TestCaseData(new LinkedListStack());
yield return new TestCaseData(new ArrayStack());