Download Project source files:ExampleFakeRepository.zip

Introduction

Here is a simple example of how to use fake repositories in test driven development. 

By using Fake Repositories generated from a binary file we are able to quickly use 'real data' in all our tests.

It is a Visual Studio 2008 solution and uses the Castle project's Active Record as an ORM.

Step 1 – Our Core Model

• SuperHero e.g. Superman
  • SupeHeroId
  • RealName
  • SuperHeroName
• Power e.g. Flight
  • PowerId
  • PowerName
• SuperHeroPower e.g. Superman’s flight
  • SuperHeroPowerId
  • Comments (e.g. Faster than a speeding bullet)

Each of our classes implements an Interface called IIdRetriever

First we define a base interface that defines all our methods needed for an ‘in-memory’ database

This base interface is called IRepository

public interface IRepository<T> where T : class
    {
        T Save(T item);
        T SaveOrUpdate(T item);
        T Get(object id);
        long Count();
        ICollection<T> FindAll(params ICriterion[] criteria);
        void Delete(T item);

    }   

Now for each class we need a repository so we define 3 repository interfaces that implement the IRepository interface with their corresponding class 

• ISuperHeroRepository
• IPowerRepository
• ISuperHeroPowerRepository

public interface ISuperHeroRepository : IRepository<SuperHero>{}

Now for the concrete implementations of our repositories the following classes are created 

• SuperHeroRepository
• PowerRepository
• SuperHeroPowerRepository

public class PowerRepository : ARRepository<Power>, IPowerRepository{}

Step 2 – Create the database, populate data and generate the binary file

In the attached project there is a command line utility project that accepts 3 arguments 

• CreateSchema – will create the tables in the designated database in the app.config
• PopulateData – will populate the tables with some sample data
• GenerateBinary – will get our ‘core’ object which contains relations to all our data and binary serialize it into a file

Step 3 – Creating our fakes for use in tests

We will now create fake ‘in-memory’ repositories which use the pre-populated binary data for use in out tests 

Firstly there are some integration tests in the database which ensure the add/edit behaviour is correct when talking to the database.

Secondly there is a folder entitled Fakes 

The main file here is the BaseRepositoryFake which contains all our base methods to mimic a database – yet in memory through an internal collection. By inheriting this class our other fake repositories get the ability to Save,SaveOrUpdate,Delete and find all.
 

Our inheriting fake repositories are as follows

• SuperHeroPowerRepositoryFake
• PowerHeroRepositoryFake
• SuperHeroPowerRepositoryFake 

These simply inherit the BaseRepositoryFake and implement their corresponding interface

public class SuperHeroRepositoryFake : BaseRepositoryFake<SuperHero>, ISuperHeroRepository
 

An explanation of the files in the root of the Tests project

• ActiveRecordFixture – singleton one time setup for active record
• RandomHelper – Set Ids and values for our fake objects (As SQL Server identity columns these will be seeded in the DB)
• SeededRepositoryFakes – contains a fake representation of each repository (e.g. SuperHeroRepository) – data is read from the binary file in these
• SeededRepositoryFakesCountTest – test to ensure the SeededRepositoryFakes are filled
• SuperHeroSeed – class that reads from the binary file

Download the above sample and run the tests to see this all in action.