public void ThrowsExceptionWhenUsernameIsEmpty()
            {
                //Arrange
                IDocumentSession session = this.DocumentStore.OpenSession();
                IAuthenticationService unitUnderTest = new AuthenticationService(session, null, null);

                //Act
                TestDelegate @delegate = () => unitUnderTest.Authenticate("", "password");

                //Assert
                Assert.Throws<ArgumentException>(@delegate);
            }
            public void ThrowsExceptionWhenUsernameDoesNotExist()
            {
                //Arrange
                IDocumentSession session = this.DocumentStore.OpenSession();
                IAuthenticationService unitUnderTest = new AuthenticationService(session, null, null);

                //Act
                TestDelegate @delegate = () => unitUnderTest.Authenticate("leRandomUsername", "lePassword");

                //Assert
                Assert.Throws<UserNotFoundException>(@delegate);
            }