state-of-tic-tac-toe: add missing test cases for invalid board states

exercises/practice/state-of-tic-tac-toe/.meta/src/reference/java/StateOfTicTacToe.java

@@ -51,6 +51,20 @@ public GameState determineState(String[] board) {
             }
         }
 
+        // If X wins, X must have played exactly one more move than O.
+        if (xWin > 0 && xCount != oCount + 1) {
+            throw new IllegalArgumentException(
+                "Impossible board: game should have ended after the game was won"
+            );
+        }
+
+        // If O wins, X and O must have played an equal number of moves.
+        if (oWin > 0 && xCount != oCount) {
+            throw new IllegalArgumentException(
+                "Impossible board: game should have ended after the game was won"
+            );
+        }
+
         if (xWin > 0 || oWin > 0) {
             return GameState.WIN;
         }
@@ -82,7 +96,6 @@ private List<String> getDiagonals(String[] board) {
         String[] diags = new String[2];
 
         for (int i = 0; i < 3; i++) {
-
             if (diags[0] == null) {
                 diags[0] = String.valueOf(board[i].charAt(i));
             } else {
@@ -108,4 +121,4 @@ private int count(char mark, String[] board) {
 
         return result;
     }
-}
+}

exercises/practice/state-of-tic-tac-toe/.meta/tests.toml

@@ -98,4 +98,4 @@ description = "Invalid boards -> Invalid board: X won and O kept playing"
 reimplements = "b1dc8b13-46c4-47db-a96d-aa90eedc4e8d"
 
 [4801cda2-f5b7-4c36-8317-3cdd167ac22c]
-description = "Invalid boards -> Invalid board: players kept playing after a win"
+description = "Invalid boards -> Invalid board: players kept playing after a win"

exercises/practice/state-of-tic-tac-toe/src/test/java/StateOfTicTacToeTest.java

@@ -95,7 +95,7 @@ public void testFinishedGameWhereXWonViaMiddleRowVictory() {
 
     @Disabled("Remove to run test")
     @Test
-    @DisplayName("Finished game where X won via middle row victory")
+    @DisplayName("Finished game where X won via bottom row victory")
     public void testFinishedGameWhereXWonViaBottomRowVictory() {
 
         assertThat(
@@ -207,7 +207,7 @@ public void testDraw() {
     @Test
     @DisplayName("Another draw")
     public void testAnotherDraw() {
-        
+
         assertThat(
             stateOfTicTacToe.determineState(new String[]{"XXO", "OXX", "XOO"})
         ).isEqualTo(GameState.DRAW);
@@ -282,4 +282,24 @@ public void testInvalidBoardPlayersKeptPlayingAfterAWin() {
             .isThrownBy(() -> stateOfTicTacToe.determineState(new String[]{"XXX", "OOO", "XOX"}))
             .withMessage("Impossible board: game should have ended after the game was won");
     }
-}
+
+    @Disabled("Remove to run test")
+    @Test
+    @DisplayName("Invalid board: O kept playing after X wins")
+    public void testInvalidBoardOKeptPlayingAfterXWins() {
+
+        assertThatExceptionOfType(IllegalArgumentException.class)
+            .isThrownBy(() -> stateOfTicTacToe.determineState(new String[]{"OO ", "XXX", " O "}))
+            .withMessage("Impossible board: game should have ended after the game was won");
+    }
+
+    @Disabled("Remove to run test")
+    @Test
+    @DisplayName("Invalid board: X kept playing after O wins")
+    public void testInvalidBoardXKeptPlayingAfterOWins() {
+
+        assertThatExceptionOfType(IllegalArgumentException.class)
+            .isThrownBy(() -> stateOfTicTacToe.determineState(new String[]{"XX ", "OOO", " XX"}))
+            .withMessage("Impossible board: game should have ended after the game was won");
+    }
+}