public async Task When_ConfirmationCode_Does_Not_Exist_Then_Null_Is_Returned()
        {
            _confirmationCodeStoreStub.Setup(c => c.Get(It.IsAny <string>(), It.IsAny <string>(), It.IsAny <CancellationToken>()))
            .Returns(() => Task.FromResult((ConfirmationCode)null));

            var result = await _authenticateResourceOwnerService
                         .AuthenticateResourceOwner("login", "password", CancellationToken.None)
                         .ConfigureAwait(false);

            Assert.Null(result);
        }