Question

My first programming job introduced me to unit testing and the concept of mock objects, but something always felt wrong about it.

Let’s say we were writing a bank app, and needed to mock a BankAccount object:

     // boilerplate code     public interface IBankAccount {         void Deposit(int amount);         void Withdrawal(int amount);         int getBalance();         int getAccountNumber();     }      public interface IBankAccountFactory {         IBankAccount getAccount(int accountNumber);     }      public class ProductionBankAccountFactory implements IBankAccountFactory {          public IBankAccount getAccount(int accountNumber) {             return new RealBankAccount(accountNumber);         }     }      public class MockBankAccountFactory implements IBankAccountFactory {         public IBankAccount getAccount(int accountNumber) {             return new MockBankAccount(accountNumber);         }     }      public static class BankAccountFactory {         // ewww, singletons!         public static IBankAccountFactory Instance;     }      // finally, my actual business objects     public class MockBankAccount implements IBankAccount {         public MockBankAccount(int accountNumber) { ... }         // interface implementation     }      public class RealBankAccount implements IBankAccount {         public RealBankAccount(int accountNumber) { ... }         // interface implementation     } 

Each class has a purpose:

• The factory and factory interfaces exist to wrap up the constructors to our mock and real objects.
• The static BankAccountFactory class allows us to assign BankAccountFactory.Instance an instance of IRealBankAccountFactory or MockBankAccountFactory at the start of our production app or tests respectively.
• Once everything is set up properly, any class can grab an instance of IBankAccount simply by calling:

     BankAccountFactory.Instance.getAccount(accountNum); 

This works, but it results in a lot of boilerplate code. I shouldn’t have to write 5 new classes for each class I want to mock. I’m convinced there’s an easier way, so I have to ask the SO community:

Is there a better or preferred way of writing mock objects?

[Edit to add:] I appreciate the links to the mocking and DI frameworks, but right now I’m working on a 500 KLOC application, and at least 60% of the code consists of the boilerplate mock classes in the style above.

I just want to reduce the size of the codebase without re-writing large chunks of code for Yet-Another-Framework™, so it helps me more to see mock classes written by hand. 🙂

Answer 1

The better way is to have someone else write it. Some options here are:

Moq – http://code.google.com/p/moq/

Rhino Mocks – http://ayende.com/projects/rhino-mocks.aspx