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There are two testing approaches that seem to work well for Entity Framework: 1. Define a repository interface that both the real repository and one or more testing repositories implement. By hiding all the interactions with the persistence framework behind the implementation of the repository interface, there is no need to create fake versions of any of the other infrastructure parts. This can simplify the implementation of the testing code, but it may leave parts of the repository itself untested.

The real object context and all the fake object contexts must implement this interface. Using this approach, you don t need to fake the entire repository, which may be difficult in some cases. Your fake object contexts don t need to mimic the behavior of the entire ObjectContext class; that would be a real challenge. You do need to limit your code to just what is available on the interfaces.

You have created a repository that manages all the queries, inserts, updates, and deletes. You want to test this repository against a real instance of the underlying database. Suppose you have a model like the one shown in Figure 8-10. Because we will create and drop the database during the tests, let s start from the beginning in a test database.

Figure 8-10. A model of books in categories To test your repository, do the following: 1. Create an empty solution. Right-click the solution in the Solution Explorer and select Add New Project. Add a new Class Library project. Name this new project BookRepository. Create a new database. Call the database Test. We ll create and drop this database in the unit tests, so make sure you create a new empty database. Add the Book and Category tables along with the relation corresponding to the model in Figure 8-10. Import these tables into a new model. Alternatively, you can use Model First to create the model; then generate the database script to create the database. Add the code in Listing 8-18. This will create a BookRepository class that handles inserts and queries against the model. Right-click the solution and select Add New Project. Select Test Project from the installed templates. Add a reference to System.Data.Entity and a project reference to BookRepository. Right-click the Test project and select Add New Test. Add a Unit Test to the Test project. Add the code in Listing 8-19 to create the tests. Right-click the Test project and select Add New Item. Select Application Configuration File from the General templates. Copy the <connectionStrings> section from the App.config file in the BookRepository project and insert it into the new App.config file in the Test project. Right-click the Test project and select Set as Startup Project. Select Debug Start Debugging or press F5 to execute the tests. Make sure there are no active connections to the Test database. Active connections will cause the DropDatabase() method to fail.

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Listing 8-18. The BookRepository class that handles inserts and queries against the model namespace BookRepository { public class BookRepository {

private TestEntities _context; public BookRepository(TestEntities context) { _context = context; } public void InsertBook(Book book) { _context.Books.AddObject(book); } public void InsertCategory(Category category) { _context.Categories.AddObject(category); } public void SaveChanges() { _context.SaveChanges(); } public IQueryable<Book> BooksByCategory(string name) { return _context.Books.Where(b => b.Category.Name == name); } public IQueryable<Book> BooksByYear(int year) { return _context.Books.Where(b => b.PublishDate.Year == year); } } } Listing 8-19. BookRepositoryTest class with the unit tests [TestClass] public class BookRepositoryTest { private TestEntities _context; [TestInitialize] public void TestSetup() { _context = new TestEntities(); if (_context.DatabaseExists()) { _context.DeleteDatabase(); } _context.CreateDatabase(); }

[TestMethod] public void TestsBooksInCategory() { var repository = new BookRepository.BookRepository(_context); var construction = new Category { Name = "Construction" }; var book = new Book { Title = "Building with Masonary", Author = "Dick Kreh", PublishDate = new DateTime(1998, 1, 1) }; book.Category = construction; repository.InsertCategory(construction); repository.InsertBook(book); repository.SaveChanges(); // test var books = repository.BooksByCategory("Construction"); Assert.AreEqual(books.Count(), 1); } [TestMethod] public void TestBooksPublishedInTheYear() { var repository = new BookRepository.BookRepository(_context); var construction = new Category { Name = "Construction" }; var book = new Book { Title = "Building with Masonary", Author = "Dick Kreh", PublishDate = new DateTime(1998, 1, 1) }; book.Category = construction; repository.InsertCategory(construction); repository.InsertBook(book); repository.SaveChanges(); // test var books = repository.BooksByYear(1998); Assert.AreEqual(books.Count(), 1); } }