The term 'Mock Objects' has become a popular one to describe special case objects that mimic real objects for testing. Most language environments now have frameworks that make it easy to create mock objects. What's often not realized, however, is that mock objects are but one form of special case test object, one that enables a different style of testing.
jMock - An Expressive Mock Object Library for Java
Mock object In object-oriented programming, mock objects are simulated objects that mimic the behavior of real objects in controlled ways. A programmer typically creates a mock object to test the behavior of some other object, in much the same way that a car designer uses a crash test dummy to simulate the dynamic behavior of a human in vehicle impacts. Reasons for use In a unit test, mock objects can simulate the behavior of complex, real objects and are therefore useful when a real object is impractical or impossible to incorporate into a unit test. If an actual object has any of the following characteristics, it may be useful to use a mock object in its place. If the real object:
Unit testing with mock objects Unit testing has become widely accepted as a "best practice" for software development. When you write an object, you must also provide an automated test class containing methods that put the object through its paces, calling its various public methods with various parameters and making sure that the values returned are appropriate. When you're dealing with simple data or service objects, writing unit tests is straightforward. However, many objects rely on other objects or layers of infrastructure. When it comes to testing these objects, it is often expensive, impractical, or inefficient to instantiate these collaborators. For example, to unit test an object that uses a database, it may be burdensome to install, configure, and seed a local copy of the database, run your tests, then tear the local database down again.
Mock Objects As an afterword to the book , we had Tim Mackinnon write up a piece on how we got here. In compensation for having been so quiet for a while, here's that chapter. Introduction The ideas and concepts behind mock objects didn't materialise in a single day. There's a long history of experimentation, discussion, and collaboration between many different developers who have taken the seed of an idea and grown it into something more profound. The final result should help you with your software development; but the background story of “The Making of Mock Objects” is also interesting—and a testament to the dedication of the people involved.
Overview EasyMock provides Mock Objects for interfaces (and objects through the class extension) by generating them on the fly using Java's proxy mechanism. Due to EasyMock's unique style of recording expectations, most refactorings will not affect the Mock Objects. So EasyMock is a perfect fit for Test-Driven Development. EasyMock : Home