What do programmers mean when they say, “Code against an interface, not an object.”?

by

Consider:

class MyClass
{
    //Implementation
    public void Foo() {}
}

class SomethingYouWantToTest
{
    public bool MyMethod(MyClass c)
    {
        //Code you want to test
        c.Foo();
    }
}

Because MyMethod accepts only a MyClass, if you want to replace MyClass with a mock object in order to unit test, you can’t. Better is to use an interface:

interface IMyClass
{
    void Foo();
}

class MyClass : IMyClass
{
    //Implementation
    public void Foo() {}
}

class SomethingYouWantToTest
{
    public bool MyMethod(IMyClass c)
    {
        //Code you want to test
        c.Foo();
    }
}

Now you can test MyMethod, because it uses only an interface, not a particular concrete implementation. Then you can implement that interface to create any kind of mock or fake that you want for test purposes. There are even libraries like Rhino Mocks’ Rhino.Mocks.MockRepository.StrictMock<T>(), which take any interface and build you a mock object on the fly.

More Related Contents:

  1. Which .NET Dependency Injection frameworks are worth looking into? [closed]
  2. C# “internal” access modifier when doing unit testing
  3. Generic Type in constructor
  4. Enterprise Library Unity vs Other IoC Containers [closed]
  5. C# – Asserting two objects are equal in unit tests
  6. How to register Windows Forms with Simple Injector
  7. Asp.Net MVC3: Set custom IServiceProvider in ValidationContext so validators can resolve services
  8. NUnit Test Run Order
  9. Can you call Directory.GetFiles() with multiple filters?
  10. What is the ‘dynamic’ type in C# 4.0 used for?
  11. execute c# code at runtime from code file
  12. How can I run an EXE program from a Windows Service using C#?
  13. How do I fix a .NET windows application crashing at startup with Exception code: 0xE0434352?
  14. How do I restart a WPF application? [duplicate]
  15. Delegate caching behavior changes in Roslyn
  16. A dictionary object that uses ranges of values for keys
  17. The State of Linkers for .NET apps (aka “Please Sir, May I have a Linker” 2009 edition)
  18. How to Combine two lambdas [duplicate]
  19. thread with multiple parameters
  20. WebClient runs javascript
  21. System.Timers.Timer Elapsed event executing after timer.Stop() is called
  22. Why can I use a collection initializer with private set access from another class?
  23. How can I include line numbers in a stack trace without a pdb?
  24. Data binding for TextBox
  25. Create object instance of a class from its name in string variable
  26. Method to determine if path string is local or remote machine
  27. Multiples Table in DataReader
  28. Async and Await with For Loop [duplicate]
  29. Understanding Covariance and Contravariance in C# 4.0
  30. caching the result from a [n async] factory method iff it doesn’t throw

Leave a Comment