Pac-Man multiplayer server - Scala & basic FP

Project is a playground for playing with simple functional programming tools in Scala to build services that are easily testable.

Testing manually using cURL

> curl -H "Content-Type: application/json" -v http://localhost:8080/backend/games -d '{ "gridName": "small" }'
{"gameId":1}
> curl http://localhost:8080/backend/games/1
{"pacMan":{"position":{"x":0,"y":0},"direction":"east"}}
> curl http://localhost:8080/backend/games/1
{"pacMan":{"position":{"x":1,"y":0},"direction":"east"}}
> curl http://localhost:8080/backend/games/1
{"pacMan":{"position":{"x":2,"y":0},"direction":"east"}}
> curl -XPUT -H "Content-Type: application/json" http://localhost:8080/games/1/direction -d '{ "newDirection": "south" }'
OK
> curl http://localhost:8080/backend/games/1
{"pacMan":{"position":{"x":2,"y":1},"direction":"south"}}

Workshop: TDDing Functional Web Apps

Get some theoretical and practical overview of the TDD approach & Functional Programming by creating a multiplayer Pac-Man game server.

• First steps in Scala and Scalatest.
• Test Driven Development (baby steps, starting with the game logic and moving towards HTTP).
• Purely functional approach (separated data and behaviors, no exceptions, ADTs, Options).
• Modeling using immutable structures.
• Separating the concerns by using functions as input parameters.
• Creating loosely coupled modules by using type parameters.
• Using function composition to connect all the dots.
• Using optics to deal with immutable changing data.

Requirements

• Familiarity with basic Scala syntax (e.g. first 2 weeks of Functional Programming Principles in Scala or Scala Tutorial)
• Please bring your laptop with Scala enabled environment and IDE. If you have problems setting them up, please use contact page

Workshop plan

Part I: Immutability (warm-up)

• theory
  • using immutable structures
  • bags of functions
• practice - GameEngine
  • review GameState and how GameEngine contains functions that get and return GameState
  • TODO: make "(not) start the game with specified grid" tests green

Part II: Introduction to stateless tests & TDD using Scalatest

• theory
  • difference between tests and TDD tests
  • using traits to easily isolate test environments
• practice - GameEngineTest
  • review already implemented tests
  • review implementation: how movePacMan evolved into "not move Pac-Man into a wall" test
  • TODO: implement "wrap Pac-Man around the grid (horizontally/vertically)" failing tests and make them green
  • TODO (optional): implement brand new "move Pac-Man in the desired direction after wall ends" failing test and make it green
  • all GameEngineTest tests should be green

Part III: Separating the concerns using functions

• theory
  • how to properly unit test the HTTP layer?
  • review entangled.StatefulHttpRoutes - hard to test means entangled concerns
  • using functions as parameters
  • abstracting over state using type parameters
• practice - HttpRoutesTest
  • live coding "(not) allow creating a new game in chosen grid configuration" test and implementation (using GameState first)
  • TODO: implement "(not) allow getting Pac-Man's state in an (unknown) existing game" failing tests and make them green
  • TODO (optional): think how would you approach using newly created HttpRoutes functions in production server
• reading:
  • blog post: Building functional & testable HTTP APIs

Part IV: Connecting all dots

• theory
  • integration tests without running a server?
• practice
  • TODO: make StatefulHttpRouteTest green

Talk: Building testable APIs with functions and meshes

Slides are available on speakerdeck.