public void ValidateCredential_WhenLoginReturnNull_ExpectDefaultUser()
        {
            _authenticationService.Setup(m => m.Login(It.IsAny <string>(), It.IsAny <string>()))
            .Returns(default(OpenLdapAppUser));

            var result = _inMemoryUserStore.ValidateCredentials("username", "password");

            Assert.Equal(default(OpenLdapAppUser), result);
            _authenticationService.VerifyAll();
        }