26329057/fakeiteasy-throws-expectationexception - Blair's passing test

gistfile1.cs

internal class JorgBTests
{
    public interface IUser
    {
        string Username { get; }
    }

    internal class UserSignupRequest
    {
        public string Username { get; set; }
        public DateTime DateOfBirth { get; set; }
        public string Password { get; set; }
    }

    public interface IDataAccessLayer
    {
        Task<bool> ExistsUserAsync(string username, CancellationToken cancellationToken);

        Task<IUser> CreateUserAsync(string username, string password, DateTime dateOfBirth,
            CancellationToken cancellationToken);
    }

    [Test]
    public void Test()
    {
        var validSignupRequest = new UserSignupRequest()
        {
            Username = "meh-spacey_space",
            DateOfBirth = DateTime.Now.Subtract(TimeSpan.FromDays(365*35)),
            Password = "someproper_passw*rd"
        };

        var testDataAccessLayer = A.Fake<IDataAccessLayer>(options => options.Strict());

        var fakeUserInstance = A.Fake<IUser>();

        A.CallTo(() => fakeUserInstance.Username).Returns(validSignupRequest.Username);
        A.CallTo(() => testDataAccessLayer.ExistsUserAsync(validSignupRequest.Username, CancellationToken.None))
            .Returns(false); // works

        A.CallTo(
            () =>
                testDataAccessLayer.CreateUserAsync(
                    validSignupRequest.Username,
                    validSignupRequest.Password,
                    validSignupRequest.DateOfBirth,
                    CancellationToken.None))
            .Returns(fakeUserInstance); // also works
    }
}