Test method inheritance with NUnit and VS Test Framework

Today I finished the implementation of the centralized exception handling demo. After adding comments to the code, I wanted to begin the related article. I decided to dedicate a post to one practice, which is test method inheritance.

How to inherit and reuse unit test methods by NUnit and Visual Studio 2008 Unit Testing Framework?

The goal is simple: keep your tests clean and avoid duplicated code.
If I have inheritance in my production code, usualy I have inheritance in my test code as well.

For example, in my application, I have the Person class and I inherit the SpanishPerson and the HungarianPerson classes from this. I don't want to test the Person, because it has only abstract methods, but I want to test the two concrete classes in the same way.


To do this:

• create a PersonTestBase class, with a _person field with Person type
  create the SpanishPersonTest and HungarianPersonTest classes


• inherit the SpanishPersonTest and HungarianPersonTest from the PersonTestBase


• if you are using VS Test Framework, make sure you don't have the [TestClass] attribute on the PersonTestBase, and add the [TestClass] attribute to the two concrete test classes


• if you are using NUnit, make sure you don't have the [TestFixture] attribute on the PersonTestBase, and add the [TestClass] attribute to the two concrete test classes


• assign the correct instance to the _person field in the SetUp/TestInitialize methods


• add generic assertions to the base test class by decorating the methods with [Test]/[TestMethod] attributes

Sorry for the stupid example, I had no better idea :)
<br />public abstract class Person<br />{<br /> public abstract string SayHello(); <br />}<br />public class SpanishPerson: Person<br />{<br /> public override string SayHello()<br /> {<br /> return "Hola";<br /> }<br />}<br />public class HungarianPerson : Person<br />{<br /> public override string SayHello()<br /> {<br /> return "Szia";<br /> }<br />}<br />

<br />public class PersonTestBase<br />{<br /> protected Person _person;<br /> protected string _expectedHello = string.Empty;<br /><br /> [TestMethod]<br /> public void SayHello_AssertValue()<br /> {<br /> string expectedValue = _expectedHello;<br /> string currentValue = _person.SayHello();<br /> Assert.AreEqual(expectedValue, currentValue);<br /> }<br />}<br /><br />[TestClass]<br />public class SpanishPersonTest : PersonTestBase<br />{<br /> [TestInitialize]<br /> public void SetUp()<br /> {<br /> _expectedHello = "Hola";<br /> _person = new SpanishPerson();<br /> }<br />}<br /><br />[TestClass]<br />public class HungarianPersonTest : PersonTestBase<br />{<br /> [TestInitialize]<br /> public void SetUp()<br /> {<br /> _expectedHello = "Szia";<br /> _person = new HungarianPerson();<br /> }<br />}<br />

Using this pattern you can avoid code duplication in your tests for classes with the same baseclass, and if you want, you can write special (non-generic) test methods in each derived test classes. The code will be cleaner, easier to understand, easier to maintain.
It's a quite easy step to improve the code quality, isn't it?