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Card game: spec and generative testingλ︎

Define a data specification that represent a deck of playing cards, adding functional specifictations to check the values passed to the functions use to play a card game.

spec generators are used to return varied sample data from those specifications. Function definitions are instrumented and check for correct arguments when those functions are called.

Create a new projectλ︎

Create a new Clojure project using :project/create from Practicalli Clojure CLI Config or add an alias definition of your choosing to the Clojure CLI user configuration.

clojure -T:project/create :template app :name practicalli/card-game

Open the src/practicalli/card_game.clj file and require the clojure.spec.alpha namespace

(ns practicalli.card-game.clj
  (:require [clojure.spec.alpha :as spec]))

Playing card specificationsλ︎

A playing card has a face value and a suit. There are 4 suits in a card deck.

A specification for the possible suits can be defined using literal values

(spec/def ::suits #{:clubs :diamonds :hearts :spades})

Define a predicate function to check a value conforms to the spec using the pattern matching that is build-in to the Clojure set data type.

(def suits? #{:clubs :diamonds :hearts :spades})

Card game decksλ︎

Suits from different regions are called by different names. Each of these suits can be their own spec.

(spec/def ::suits-french #{:hearts :tiles :clovers :pikes})
(spec/def ::suits-german #{:hearts :bells :acorns :leaves})
(spec/def ::suits-spanish #{:cups :coins :clubs :swords})
(spec/def ::suits-italian #{:cups :coins :clubs :swords})
(spec/def ::suits-swiss-german #{:roses :bells :acorns :shields})

A composite specification called ::card-suits provides a simple abstraction over all the variations of suits. Using ::card-suits will be satisfied with any region specific suits.

(spec/def ::card-suits
  (spec/or :french ::suits-french
           :german ::suits-german
           :spanish ::suits-spanish
           :italian ::suits-italian
           :swiss-german ::suits-swiss-german
           :international ::suits-international))

Define an aliasλ︎

Jack queen king are called face cards in the USA and occasionally referred to as court cards in the UK.

Define a spec for ::face-cards and then define :court-cards and alias

(spec/def ::face-cards #{:jack :queen :king :ace})
(spec/def ::court-cards ::face-cards)

Any value that conforms to the ::face-card specification also conforms to the ::court-cards specification.

(spec/conform ::court-cards :ace)

Playing card rankλ︎

Each suit in the deck has the same rank of cards explicitly defining a rank

(spec/def ::rank #{:ace 2 3 4 5 6 7 8 9 10 :jack :queen :king})

Rank can be defined more succinctly with the clojure.core/range function. The expression (range 2 11) will generates a sequence of integer numbers from 2 to 10 (the end number is exclusive, so 11 is not in the sequence).

Using clojure.core/into this range of numbers can be added to the face card values.

(into #{:ace :jack :queen :king} (range 2 11))

The ::rank specification now generates all the possible values for playing cards.

(spec/def ::rank (into #{:ace :jack :queen :king} (range 2 11)))

The specification only checks to see if a value is in the set, the order of the values in the set is irrelevant.

Playing Cardλ︎

A playing card is a combination of suit and face value, a pair of values, referred to as a tuple.

Clojure spec has a tuple function, however, we need to define some predicates first

(spec/def ::playing-card (spec/tuple ::rank ::suits ))

Use the spec with values to see if they conform. Try you own values for a playing card.

(spec/conform ::playing-card [:ace :spades])

Game specsλ︎

Define specifications for data used to represent players and the overall card game.

The player name is a very simple spec.

(spec/def ::name string?)

Score will keep a running total of a player score across games, again a simple integer value.

(spec/def ::score int?)

A player is represented by a hash-map that contains their name, score and the hand they are currently dealt. The hand is a collection of tuples representing a playing card.

(spec/def ::player
            :req [::name ::score ::dealt-hand]))

Game deck specsλ︎

A card game has a deck of 52 cards, one card for each combination of suit and rank.

The size of the card deck changes over the course of a game, so the deck can contain any number of cards. The deck must contain only cards to be valid.

(spec/def ::card-deck (spec/* ::playing-card))

At this stage in the design, a card game can have any number of players

(spec/def ::players (spec/* ::player))

A game is represented by a hash-map with a collection of players and a card deck

(spec/def ::game (spec/keys :req [::players ::card-deck]))

Generative data from Specificationsλ︎

Clojure spec can generate random data which conforms to a specification, highly useful in testing Clojure code with a wide variety of values.

  • clojure.spec.alpha/gen returns a generator for the given specification.
  • clojure.spec.gen.alpha/generate takes that generator and creates a random value that conforms to the specification.
  • clojure.spec.gen.alpha/sample will generate a collection of random values that each conform to the specification.

Require the clojure spec namespaces to make use of their functions.

(ns practicalli.card-game.clj
  (:require [clojure.spec.alpha :as spec]
            [clojure.spec.gen.alpha :as spec-gen]
            [clojure.spec.test.alpha :as spec-test]))

(spec/def ::suits #{:clubs :diamonds :hearts :spades})
(spec/def ::rank #{:ace 2 3 4 5 6 7 8 9 10 :jack :queen :king})

To generated data based on a specification, first get a generator for a given spec,

(spec/gen ::suits)

generate will return a value using the specific generator for the specification.

(spec-gen/generate (spec/gen ::suits))

sample will generate a number of values from the given specification

(spec-gen/sample (spec/gen ::rank))

Card Game dataλ︎

Generate a random value for the ::player specification

(spec-gen/generate (spec/gen ::player))

Expected output from generate ```clojure


{:name "Yp34KE63vAL1eriKN4cBt", :score 225, :dealt-hand ([9 :hearts] [4 :clubs] [8 :hearts] [10 :clubs] [:queen :spades] [3 :clubs] [6 :hearts] [8 :hearts] [7 :diamonds] [:king :spades] [:ace :diamonds] [2 :hearts] [4 :spades] [2 :clubs] [6 :clubs] [8 :diamonds] [6 :spades] [5 :spades] [:queen :clubs] [:queen :hearts] [6 :spades])}


Generate a random value for the ::game specification

(spec-gen/generate (spec/gen ::game))

Generate a collection of random values that each conform to the specification.

(spec-gen/sample (spec/gen ::game))

Function Specificationsλ︎

A function specification can contain a specification for the arguments, the return values and the relationship between the two.

The specifications for the function may be composed from previously defined data specifications.

(ns practicalli.card-game
  (:require [clojure.spec.alpha :as spec]
            [clojure.spec.gen.alpha :as spec-gen]
            [clojure.spec.test.alpha :as spec-test]))

(spec/def ::suit #{:clubs :diamonds :hearts :spades})
(spec/def ::rank (into #{:jack :queen :king :ace} (range 2 11)))
(spec/def ::playing-card (spec/tuple ::rank ::suit))
(spec/def ::dealt-hand (spec/* ::playing-card))

(spec/def ::name string?)
(spec/def ::score int?)
(spec/def ::player (spec/keys :req [::name ::score ::dealt-hand]))
(spec/def ::card-deck (spec/* ::playing-card))
(spec/def ::players (spec/* ::player))
(spec/def ::game (spec/keys :req [::players ::card-deck]))

Function definitionλ︎

The card game application has three functions to start with.

(defn regulation-card-deck
  "Generate a complete deck of playing cards"
  [{:keys [::deck ::players] :as game}]
  (apply + (count deck)
         (map #(-> % ::delt-hand count) players)))

At the start of function design, the algorithm may still be undefined. Using the specifications and generators mock data can be returned as a placeholder.

(defn deal-cards
  "Deal cards to each of the players
   Returns updated game hash-map"
  (spec-gen/generate (spec/gen ::game)))
(defn winning-player
  "Calculate winning hand by comparing each players hand
  Return winning player"
  (spec-gen/generate (spec/gen ::player)))

The expected form of a player won game:

  {:name      "Jenny Nada",
   :score     225,
   :dealt-hand [[9 :hearts] [4 :clubs] [8 :hearts] [10 :clubs] [:queen :spades]]}

Spec definitionsλ︎

Define a function specification for the deal-cards function

  • argument must be of type ::game
  • return type is ::game
  • function applies arguments to a game and returns the game
(spec/fdef deal-cards
  :args (spec/cat :game ::game)
  :ret ::game
  :fn #(= (regulation-card-deck (-> % :args :game))
          (regulation-card-deck (-> % :ret))))

Define a function specification for the winning-player function

  • argument must be of type ::players
  • return type is ::players
(spec/fdef winning-player
  :args (spec/cat :players ::players)
  :ret ::player)

Instrument functionsλ︎

Instrumenting functions will wrap a function definition and check the arguments of any call to the instrumented function.

(spec-test/instrument `deal-cards)

Calling the deal-cards function with an incorrect argument returns an error that describes where in the specification the error occurred.

(deal-cards "fake game data")

Error in an easier to read format

ERROR: #error
 {:message "Call to #'practicalli.card-game/deal-cards did not conform to spec:\n\
 "fake game data\" - failed:
 map? in: [0] at: [:args :game] spec: :practicalli.card-game/game\n",
 :data {:cljs.spec.alpha/problems
 [{:path [:args :game],
   :pred cljs.core/map?,
   :val "fake game data",
   :via [:practicalli.card-game/game :practicalli.card-game/game],
   :in [0]}],
 :cljs.spec.alpha/spec #object[cljs.spec.alpha.t_cljs$spec$alpha17968],
 :cljs.spec.alpha/value ("fake game data"),
 :cljs.spec.alpha/args ("fake game data"),
 :cljs.spec.alpha/failure :instrument}}

Organizing function instrumentationλ︎

Instrumenting functions creates a wrapper around the original function definition.

When you change the function definition and evaluate the new code, it replaces the instrumentation of the function. Therefore each time a function is redefined it should be instrumented.

There is no specific way to manage instrumenting a function, however, a common approach is to define a collection of functions to instrument, then use a helper function to instrument all the functions at once.

Bind a name to the collection of function specifications.

(def ^:private function-specifications

Define a simple helper function to instrument all the functions in the collection.

(defn instrument-all-functions
  (spec-test/instrument function-specifications))

Refactoring the code may involve a number of changes benefit from instrumentation being switched off until its complete. The unstrument function will remove instrumentation from all the functions in the collection.

(defn unstrument-all-functions
  (spec-test/unstrument function-specifications))

Koacha Test Runner can include functional specifications

Koacha test runner can manage the testing of function specifications and is especially useful for managing unit level testing with specifications.

Last update: April 25, 2023