diff --git a/src/test/kotlin/eventDemo/app/event/projection/GameStateTest.kt b/src/test/kotlin/eventDemo/app/event/projection/GameStateTest.kt
index 78545a8..ad789b4 100644
--- a/src/test/kotlin/eventDemo/app/event/projection/GameStateTest.kt
+++ b/src/test/kotlin/eventDemo/app/event/projection/GameStateTest.kt
@@ -1,15 +1,159 @@
 package eventDemo.app.event.projection
 
+import eventDemo.business.entity.Card
+import eventDemo.business.entity.Deck
+import eventDemo.business.entity.Discard
+import eventDemo.business.entity.GameId
+import eventDemo.business.entity.Player
+import eventDemo.business.entity.PlayersHands
+import eventDemo.business.event.projection.GameState
 import io.kotest.core.spec.style.FunSpec
+import io.kotest.matchers.equals.shouldBeEqual
 
 class GameStateTest :
   FunSpec({
-    xtest("isReady") { }
-    xtest("nextPlayer") { }
+    val player1 = Player("Tesla")
+    val player2 = Player("Einstein")
+
+    test("isReady return false when all players in the game is not ready") {
+      GameState(
+        aggregateId = GameId(),
+        players = setOf(player1, player2),
+        readyPlayers = setOf(player1),
+      ).isReady shouldBeEqual false
+    }
+
+    test("isReady return true when all players in the game is ready") {
+      GameState(
+        aggregateId = GameId(),
+        players = setOf(player1, player2),
+        readyPlayers = setOf(player1, player2),
+      ).isReady shouldBeEqual true
+    }
+
     xtest("nextPlayerTurn") { }
     xtest("playerDiffIndex") { }
     xtest("cardOnBoardIsForYou") { }
     xtest("playableCards") { }
     xtest("playerHasNoCardLeft") { }
-    xtest("canBePlayThisCard") { }
+
+    test("canBePlayThisCard return true when a card can be played on the current game") {
+      canBePlayThisCard(
+        onTheDeck = Card.NumericCard(0, Card.Color.Red),
+        playedCard = Card.NumericCard(5, Card.Color.Red),
+      ) shouldBeEqual true
+
+      canBePlayThisCard(
+        onTheDeck = Card.NumericCard(0, Card.Color.Red),
+        playedCard = Card.NumericCard(0, Card.Color.Blue),
+      ) shouldBeEqual true
+
+      canBePlayThisCard(
+        onTheDeck = Card.NumericCard(0, Card.Color.Red),
+        playedCard = Card.NumericCard(0, Card.Color.Green),
+      ) shouldBeEqual true
+
+      canBePlayThisCard(
+        onTheDeck = Card.NumericCard(0, Card.Color.Red),
+        playedCard = Card.Plus2Card(Card.Color.Red),
+      ) shouldBeEqual true
+
+      canBePlayThisCard(
+        onTheDeck = Card.NumericCard(0, Card.Color.Red),
+        playedCard = Card.Plus2Card(Card.Color.Red),
+      ) shouldBeEqual true
+
+      canBePlayThisCard(
+        onTheDeck = Card.NumericCard(0, Card.Color.Red),
+        playedCard = Card.Plus4Card(),
+      ) shouldBeEqual true
+
+      canBePlayThisCard(
+        onTheDeck = Card.Plus4Card(),
+        playedCard = Card.Plus4Card(),
+      ) shouldBeEqual true
+
+      canBePlayThisCard(
+        onTheDeck = Card.Plus4Card(),
+        playedCard = Card.Plus4Card(),
+      ) shouldBeEqual true
+
+      canBePlayThisCard(
+        onTheDeck = Card.Plus2Card(Card.Color.Red),
+        playedCard = Card.Plus2Card(Card.Color.Blue),
+      ) shouldBeEqual true
+
+      canBePlayThisCard(
+        onTheDeck = Card.NumericCard(0, Card.Color.Red),
+        playedCard = Card.ChangeColorCard(),
+      ) shouldBeEqual true
+
+      canBePlayThisCard(
+        onTheDeck = Card.ReverseCard(Card.Color.Red),
+        playedCard = Card.NumericCard(0, Card.Color.Red),
+      ) shouldBeEqual true
+    }
+
+    test("canBePlayThisCard return false when a card cannot be played on the current game") {
+      canBePlayThisCard(
+        onTheDeck = Card.NumericCard(0, Card.Color.Red),
+        playedCard = Card.NumericCard(9, Card.Color.Blue),
+      ) shouldBeEqual false
+
+      canBePlayThisCard(
+        onTheDeck = Card.NumericCard(0, Card.Color.Red),
+        playedCard = Card.Plus2Card(Card.Color.Blue),
+      ) shouldBeEqual false
+
+      canBePlayThisCard(
+        onTheDeck = Card.NumericCard(0, Card.Color.Red),
+        playedCard = Card.Plus2Card(Card.Color.Blue),
+      ) shouldBeEqual false
+
+      canBePlayThisCard(
+        onTheDeck = Card.Plus2Card(Card.Color.Red),
+        playedCard = Card.Plus4Card(),
+      ) shouldBeEqual false
+
+      canBePlayThisCard(
+        onTheDeck = Card.Plus2Card(Card.Color.Red),
+        playedCard = Card.ChangeColorCard(),
+      ) shouldBeEqual false
+
+      canBePlayThisCard(
+        onTheDeck = Card.Plus2Card(Card.Color.Red),
+        playedCard = Card.NumericCard(0, Card.Color.Red),
+      ) shouldBeEqual false
+    }
   })
+
+private fun canBePlayThisCard(
+  onTheDeck: Card,
+  playedCard: Card,
+): Boolean {
+  val player1 = Player("Tesla")
+  return gameStateWithCard(
+    player = player1,
+    onTheDeck = onTheDeck,
+    playerHand = listOf(playedCard),
+  ).canBePlayThisCard(player1, playedCard)
+}
+
+private fun gameStateWithCard(
+  player: Player,
+  onTheDeck: Card,
+  playerHand: List<Card>,
+): GameState {
+  val player2 = Player("Einstein")
+  return GameState(
+    aggregateId = GameId(),
+    players = setOf(player, player2),
+    readyPlayers = setOf(player, player2),
+    lastCardPlayer = player2,
+    deck =
+      Deck(
+        discard = Discard(setOf(onTheDeck)),
+        playersHands = PlayersHands(mapOf(player.id to playerHand)),
+      ),
+  )
+}