Trip Service Kata

Kata for legacy code hands-on session. The objective is to test and refactor the legacy TripService class.

The end result should be well-crafted code that express the domain.

TripService.getTripsByUser is a use case to return a list of trips from your single friend.

Lesson 1 - Extract and Override

TripService.getTripsByUser is a use case to return a list of trips from your single friend.

Extract all the dependencies with side effects related code to make TripService.getTripsByUser testable.

✅ Expected output:

• Pass all tests:
  • It should get a list of trips from a user if the user is your friend
  • It should not get a list of trips from a user if the user is not your friend
  • It should throw UserNotLoggedInException if you are not logged in
• Two extra protected methods to in TripService

Tips in case you need

1. Highlight the part to `getLoggedUser` and do `Extract Method` to replace with a new protected method

2. Highlight the part to `findTripsByUser` and do `Extract Method` to replace with a new protected method

3. Create a test file

4. In the test file, create a child class of `TripService` and override the two protected methods mentioned above to return fixed data

5. In the test file, create some test cases with some fake data.

Lesson 2 - Extract Interface

Extract Interface from the dependencies with side effects of TripService to make TripService.getTripsByUser testable and detectable (able to be sensed)

✅ Expected output:

• Pass all tests:
  • It should get a list of trips from a user if the user is your friend
  • It should not get a list of trips from a user if the user is not your friend
  • It should throw UserNotLoggedInException if you are not logged in
• Two extra interfaces

Tips in case you need

1. Create an interface `IUserSession` and put methods you need in `UserSession` into it.

2. Make the `UserSession` implements the interface

3. Create an interface `ITripDAO` and put methods you need in `TripDAO` into it.

4. Make the `TripDAO` implements the interface

5. Create a test file

6. In the test file, create subclasses of the two interfaces mentioned above and return fixed data.

7. In the test file, create a test case to make it fail

8. In the `TripService`, dependency inject the two modules into the constructor of the `TripService`

9. In the `TripService`, change the dependency modules to the interface.

10. Go back to the tests, pass the subclasses you created in step 6 to the test cases and make tests pass.

Lesson 3 - Make changes

For privacy concerns, we want to add an attribute public to Trip which is true by default. If the trip.public is false, then even your friends cannot access this trip by TripService.getTripsByUser.

Specification by example:

  Scenario: You cannot access trips that was not public event though the owner is your friend
    Given Foo is Bar's friend
    And Bar has trips:
      | trip | public |
      | Ta   | true   |
      | Tb   | false  |
    When Foo request Bar's trip list
    Then it should display Ta only

Retrospective

• Discuss the difference between extract and override and extract interface
  • Why to use
  • When to use
• Did you use the IDE refactor tools? How do you think about them?
• Does tests help you build confidence to make changes to code?
• Is there any possible to improve your tests in readability and maintainability?

Advanced Lessons

Notes

1. Use refactor tools as many as you can to prevent manually modification.
2. Make sure your results and changes are covered by tests