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This walkthrough will demonstrate how to use the new Plain Old CLR Object (POCO) support in Entity Framework 4.0 to develop an application using Test-Driven Development (TDD).

In the first release of EF, entity classes had to inherit from EntityObject or implement one of the EF interfaces, which meant your classes had to have direct dependencies on the EF. As a result, writing unit tests that verified the logic for just your domain objects was challenging. The tests would have to interact with the database directly, which violates the principle of persistence ignorance, and results in the tests running orders of magnitude slower.

With Entity Framework 4.0, you can use the Repository and Unit of Work pattern to create domain entities that are completely EF-agnostic. With the hard dependency on the EF removed, it’s much easier to create fakes and mocks of these objects when writing unit tests. These tests no longer need to hit the database at all, offering a clean separation of concerns, reducing complexity, and making unit tests run significantly faster.

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