What is this?

A single T4 file that mocks your Linq to SQL data context and lets you write tests against an in-memory version of it.

Setup

1. Copy Rename.extensions.tt into your project, in the same folder as your DBML
2. Rename Rename.extensions.tt to [YourDBMLName].extensions.tt

How to use it

Say your data context is called ExampleDataContext. The mock data context will be called MemoryExampleDataContext. You can use it just like you would your normal data context—it will have all the same tables. Everything is stored in memory, so it's very fast for testing.

using(var db = new MemoryExampleDataContext()) {
  db.Products.InsertOnSubmit(new Product { SKU = "example" });
  db.SubmitChanges();
  
  Console.WriteLine(db.Products.First().SKU);
  // prints "example"
}

The interface that makes this all testable is called I[YourDBMLName]DataContext. If you have code that's using a concrete type of ExampleDataContext...

public static List<Product> GetProducts(ExampleDataContext db) {
  return db.Products().ToList();
}

... you can make it testable by using the interface IExampleDataContext.

public static List<Product> GetProducts(IExampleDataContext db) {
  return db.Products().ToList();
}

That way, you can call GetProducts with a MemoryExampleDataContext for testing, and a real ExampleDataContext in production.