Creating test for refactoring legacy code.

Creating test for refactoring legacy code.

1. We may not change production code if not covered by tests.
2. Start testing the legacy code following the shortest branch.
3. We should not invoke more classes than the one being under test.
4. We try to create a fluent interface. If we are testing user is not logged in, our test must
set the value making the not logged in user (we will call it GUEST)
5. Making clear that the input parameter in getTripsByUser is useless for the Unit Test throw_an_exception_when_user_is_not_logged_in