feat: added computed property for trick

Cards/Sources/Hearts/Hearts.swift

@@ -3,6 +3,9 @@ import Combine
 
 public final class Hearts: ObservableObject {
     @Published private(set) var players: [Player]
+    var trick: [PlayingCard] {
+        players.compactMap(\.selectedCard)
+    }
 
     public init(players: Int) {
         self.players = Deck.hearts(playerCount: players)

Cards/Sources/Hearts/Player.swift

@@ -5,6 +5,9 @@ public final class Player: ObservableObject {
     @Published
     public private(set) var hand: [PlayingCard]
 
+    @Published
+    public private(set) var selectedCard: PlayingCard?
+
     @Published
     public private(set) var score: Int
     private let scoringSystem = HeartsScore()
@@ -23,9 +26,11 @@ public final class Player: ObservableObject {
             preconditionFailure("Cannot play a card that is not in your hand")
         }
         hand.remove(at: index)
+        selectedCard = card
     }
 
     func pickUp(cards: [PlayingCard]) {
+        selectedCard = nil
         score = cards
             .map(scoringSystem.score)
             .reduce(score, +)

Cards/Tests/HeartsTests/HeartsTrickTests.swift

@@ -0,0 +1,16 @@
+import CardsModel
+@testable import Hearts
+import XCTest
+
+final class HeartsTrickTests: XCTestCase {
+    func testTrick() {
+        let sut = Hearts(players: 4)
+        XCTAssertTrue(sut.trick.isEmpty)
+
+        let playerOne = sut.players[0]
+        let card = playerOne.hand[0]
+        playerOne.play(card: card)
+
+        XCTAssertEqual(sut.trick, [card])
+    }
+}

Cards/Tests/HeartsTests/PlayerTests.swift

@@ -50,3 +50,20 @@ final class PlayerTests: XCTestCase {
         XCTAssertTrue(sut.shotForTheMoon)
     }
 }
+
+extension PlayerTests {
+    func testPlayCard() {
+        let sut = Player(hand: [
+            .suited(.five, .diamonds),
+            .suited(.jack, .spades)
+        ])
+
+        sut.play(card: .suited(.five, .diamonds))
+        XCTAssertEqual(sut.selectedCard, .suited(.five, .diamonds))
+        XCTAssertEqual(sut.hand, [.suited(.jack, .spades)])
+
+        sut.play(card: .suited(.jack, .spades))
+        XCTAssertEqual(sut.selectedCard, .suited(.jack, .spades))
+        XCTAssertEqual(sut.hand, [])
+    }
+}