Trip belongs to a Line.
Line name must be case insensitive.
Refactor tests.
Remove unused var.
Added City class.
Composer update.
Improving getName in City.
Refactor tests.
City name must be a string.
Refactor tests.
Creating Route class.
Refactor tests.
Slug can't be empty.
Slug must be a string.
Refactor tests.
Change field name.
Add id field to Route.
Refactor tests.
Check for valid Ids.
Improve id validation.