Small changes

Small changes Examples:

• Method that save new user in DB
• Service that validate user details
• HTTP POST route that create the user (only call the service method)

Big change Example

Create new POST route that create the user,
Including all needed code in:

• Http level (controller)
• Service level
• DAL level

Small changes advantages

• Early feedback
• Quick and efficient code review
• Early code merge
• Easy merges

Test come along with functionality

• For any such small change we merge it's test as part of the changeset (Pull Request)
• Sometimes the test is just unit test/s and sometimes it include component or even end-to-end tests

Test First Development

Write the tests before you write the code.

Some advantages:

• Test is already there when functionality is done
• Making sure test really test something
  (failed when functionality is missing)
• Declare method signature/API before coding it
• Enabler for refactor

Top Down / Bottom Up

Use latest city weather - Bottom Up

• Introduce FavoritesService with set/get last city
• Use favorite service in WeatherService
• (controller level - test that validate the functionality)
• Change FE to consume weather REST API without city upon loading

Use latest city weather - Top Down

• Change FE to consume weather REST API without city upon loading
• Controller level - support REST API without city - return last city
• Move last city functionality down to WeatherService
• Introduce FavoritesService with set/get last city
• Use favorite service in WeatherService for get/set the last city

Exercise 1 - small changes

• fork trunk-base-workshop git
• Checkout branch lesson1/exercise-1-start
• Change the code so by default the user will get forecast of his current location
• Commit and push little changes covered by tests
• Choose strategy: top-down or bottom-up

Exercise 1 - some tips

• Use openweathermap API for weather and forecast
• You might use the following frontend code for getting the user location:

  
  function getCurrentLocation() {
    return new Promise(function(resolve, reject) {
      navigator.geolocation.getCurrentPosition(resolve, reject);
    });
  }
                      

Branch By Abstraction

Branch By Abstraction definition

"Branch by Abstraction" is a technique for making a large-scale change to a software system in gradual way that allows you to release the system regularly while the change is still in-progress.

Branch By Abstraction step by step

• There is a piece of code you want to change, the code is consumed elsewhere in your system
• Create an abstraction of this code (e.g. extract an interface)
• Make the consumers of this code to consume the abstraction instead of concrete implementation
• Create the change you want to make as another implementation (supplier). Implement it in small steps

Branch By Abstraction step by step - cont

• Once the new implementation is ready switch the system to use it (or use feature toggle)
• Clean leftover while needed (like removed previous implementation)

Illustration by Martin Fowler

Dependency Injection

• Dependency injection is a technique in which an object receives other objects that it depends on.
• These other objects are called dependencies.
• In the typical "using" relationship the receiving object is called a client and the passed (that is, "injected") object is called a service.

Wikipedia

Exercise 2 - react branch by abstraction

• Checkout branch lesson2/exercise-2-start
• Change the code so instead of weather icon user will see emojis icons
• use emoji-css.afeld.me for that
• merge small changes by using branch by abstraction

Feature Toggles

Feature Toggles definition

A feature toggle (also feature flag) is a technique in software development that attempts to provide an alternative to maintaining multiple branches in source code (known as feature branches), such that a software feature can be tested even before it is completed and ready for release.

Feature Toggles definition - cont

A feature toggle is used to hide, enable or disable the feature during runtime. For example, during the development process, a developer can enable the feature for testing and disable it for other users.

Feature Toggles alternate definition

A "if" statement in the code that wrap the feature's code

Feature Toggles benefits

• Merge “Half Baked” Features / small commits
• Agility of Delivering Feature
• Test in CI from First Day
• Early Feedback
• Experimental Features
• Handling Vague Release Program

new Feature (Toggle) Life cycle

• Instead of creating new feature branch create a new feature toggle
• Set the toggle state to off
• Merge the new toggle code to main branch
• Develop your code in small commits and merge it to main branch

new Feature (Toggle) Life cycle - cont

• Once the feature is ready enough, enable the toggle in CI / test env
• Once the feature is completely ready and the code is running in production - enable the toggle in production
• Once the clients are happy with the feature, remove the toggle from code and from management tool

new Feature (Toggle) Life cycle

Feature Toggles Frameworks

• Unleash
• Cloudbees/Rollout
• AT&T IXP

Exercise 3 - final exercise

• In this exercise you will work as a team on multiple tasks
• Make sure you are using small commits for better interaction
• Choose one the team member fork so you would work on the same fork
• Checkout branch lesson3/exercise-3-start

Exercise 3 - final exercise - favorites per user

• Add support to save the favorites in some persistent storage (file/mongo). You might use branch by abstraction for that
• Support login to the app so you can identify each user
• By default show to the user the latest place he used (instead of his location)
• Bonus - add favorites option to the user and to store and show his favorites places