下面一个是这样做的只有一个办法：

The below one is only one way of doing this:

public class FooController : ApiController {

    public string Get() {

        return User.Identity.Name;
    }
}

public class FooTest {

    [Fact]
    public void Foo() {

        var identity = new GenericIdentity("tugberk");
        Thread.CurrentPrincipal = new GenericPrincipal(identity, null);
        var controller = new FooController();

        Assert.Equal(controller.Get(), identity.Name);
    }
}