Custom Dummy Creation

FakeItEasy has built-in Dummy creation rules that provide usable non-null values to be used in tests. However, if the default dummy creation behavior isn't adequate, you can provide your own. Here's an example:

class DummyBookDefinition : DummyDefinition<Book>
{
    protected override Book CreateDummy()
    {
        return new Book { Title = "Some Book", PublishedOn = new DateTime(2000, 1, 1) };
    }
}

How it works

FakeItEasy uses classes that implement the following interface to create Dummies:

public interface IDummyDefinition
{
    Type ForType { get; }
    object CreateDummy();
}

When FakeItEasy tries to create a Dummy, it looks at all known IDummyDefinition implementations and if one of them has a ForType that matches the desired type, CreateDummy is used.

Although it's possible to implement IDummyDefinition explicitly, the preferred approach is to extend abstract class DummyDefinition<T>: IDummyDefinition, where T is the type of dummy to produce, as in the example above. DummyDefinition<T> implements ForType (returning T), so all that's needed is to implement the abstract CreateDummy method, having it return the Dummy.

How does FakeItEasy find the Dummy Definitions?

On initialization, FakeItEasy looks for Discoverable Extension Points, including Dummy Definitions.