public class Adder
{
    public virtual int Add(int operand1, int operand2)
    {
        return operand1 + operand2;
    }
}

public class AdvancedAdder : Adder
{
}

public abstract class AdderUnitTestsBase
{
    protected static Adder Adder;

    [DataTestMethod]
    [DataRow(2, 2, 4)]
    [DataRow(-1, 2, 1)]
    [DataRow(2, -3, -1)]
    [DataRow(0, 0, 0)]
    public void Add_ReturnsCorrectResult(
        int operand1, int operand2, int result)
    {
        Assert.AreEqual(result, Adder.Add(operand1, operand2));
    }
}


[TestClass]
public class AdderUnitTests : AdderUnitTestsBase
{
    [ClassInitialize]
    public static void ClassInit(TestContext context)
    {
        Adder = new Adder();
    }
}

[TestClass]
public class AdvancedAdderUnitTests : AdderUnitTestsBase
{
    [ClassInitialize]
    public static void ClassInit(TestContext context)
    {
        Adder = new AdvancedAdder();
    }
}

public class AdvancedAdder : Adder
{
    public int Add(int operand1, int operand2, int operand3)
    {
        return operand1 + operand2 + operand3;
    }

    public uint Add(uint operand1, uint operand2)
    {
        return operand1 + operand2;
    }
}

public class AdvancedAdder : Adder
{
    public override int Add(int operand1, int operand2)
    {
        return operand1 - operand2;
    }
}

public void method()
{
    switch (this.getType().Name)
    {
        case "Square":
            // do the square thing
            break;
        case "Rectangle":
            // do the rectangle thing
            break;
    }
}

PARENT
  ^
  |
CHILD