diff --git a/src/model/Board.java b/src/model/Board.java
index f4a753d..05374fc 100644
--- a/src/model/Board.java
+++ b/src/model/Board.java
@@ -1,10 +1,19 @@
 package model;
 
 public class Board {
+    Player[] boxes = new Player[9];
     public void setBox(int column, int row, Player value) {
+        int index = getIndex(column, row);
+        boxes[index] = value;
     }
 
     public Player getBox(int column, int row) {
-        return null;
+        int index = getIndex(column, row);
+        return boxes[index];
+    }
+
+    private int getIndex(int column, int row) {
+        if (row < 1 || row > 3) throw new IndexOutOfBoundsException();
+        return (column - 1) * 3 + row - 1;
     }
 }
diff --git a/src/model/InputChecker.java b/src/model/InputChecker.java
index f289010..5745960 100644
--- a/src/model/InputChecker.java
+++ b/src/model/InputChecker.java
@@ -2,6 +2,10 @@ package model;
 
 public class InputChecker {
     public boolean isInputValid(Board board, int box) {
-        return false;
+        if (box < 1 || box > 9) return false;
+        int col = (box - 1) / 3 + 1;
+        int row = box % 3;
+        if (row == 0) row = 3;
+        return board.getBox(col, row) == null;
     }
 }
diff --git a/src/model/WinChecker.java b/src/model/WinChecker.java
index 0d536dd..aaa8326 100644
--- a/src/model/WinChecker.java
+++ b/src/model/WinChecker.java
@@ -2,10 +2,87 @@ package model;
 
 public class WinChecker {
     public boolean isGameOver(Board b) {
-        return false;
+        if (b.getBox(1, 1) != null) {
+            if (b.getBox(1, 1) == b.getBox(1, 2)
+                    && b.getBox(1, 2) == b.getBox(1, 3))
+                return true;
+            if (b.getBox(1, 1) == b.getBox(2, 1)
+            && b.getBox(1, 1) == b.getBox(3, 1))
+                return true;
+            if (b.getBox(1, 1) == b.getBox(2, 2)
+                    && b.getBox(1, 1) == b.getBox(3, 3))
+                return true;
+        }
+        if (b.getBox(3, 1) != null) {
+            if (b.getBox(3, 1) == b.getBox(3, 2)
+                    && b.getBox(3, 1) == b.getBox(3, 3))
+                return true;
+            if (b.getBox(3, 1) == b.getBox(2, 2)
+                    && b.getBox(3, 1) == b.getBox(1, 3))
+                return true;
+        }
+        if (b.getBox(2, 1) != null
+            && b.getBox(2, 1) == b.getBox(2, 2)
+            && b.getBox(2, 1) == b.getBox(2, 3))
+            return true;
+        if (b.getBox(1, 2) != null
+                && b.getBox(1, 2) == b.getBox(2, 2)
+                && b.getBox(1, 2) == b.getBox(3, 2))
+            return true;
+        if (b.getBox(1, 3) != null
+                && b.getBox(1, 3) == b.getBox(2, 3)
+                && b.getBox(1, 3) == b.getBox(3, 3))
+            return true;
+        for (int i = 1; i <= 3; ++i)
+            for (int j = 1; j <= 3; ++j)
+                if (b.getBox(i, j) == null)
+                    return false;
+        return true;
     }
 
-    public Player getWinner(Board b) {
-        return null;
+    public Player getWinner(Board b) throws IllegalGameStateException {
+        Player currentBox, winner = null;
+        currentBox = b.getBox(1, 1);
+        if (currentBox != null) {
+            if (currentBox == b.getBox(1, 2)
+                    && currentBox == b.getBox(1, 3))
+                winner = currentBox;
+            if (currentBox == b.getBox(2, 1)
+                    && currentBox == b.getBox(3, 1))
+                winner = currentBox;
+            if (currentBox == b.getBox(2, 2)
+                    && currentBox == b.getBox(3, 3))
+                winner = currentBox;
+        }
+        currentBox = b.getBox(3, 1);
+        if (currentBox != null) {
+            if (currentBox == b.getBox(3, 2)
+                    && currentBox == b.getBox(3, 3)) {
+                if (winner != null && winner != currentBox) throw new IllegalGameStateException();
+                winner = currentBox;
+            }            if (currentBox == b.getBox(2, 2)
+                    && currentBox == b.getBox(1, 3)) {
+                if (winner != null && winner != currentBox) throw new IllegalGameStateException();
+                winner = currentBox;
+            }        }
+        currentBox = b.getBox(2, 1);
+        if (currentBox != null
+                && currentBox == b.getBox(2, 2)
+                && currentBox == b.getBox(2, 3)) {
+            if (winner != null && winner != currentBox) throw new IllegalGameStateException();
+            winner = currentBox;
+        }        currentBox = b.getBox(1, 2);
+        if (currentBox != null
+                && currentBox == b.getBox(2, 2)
+                && currentBox == b.getBox(3, 2)) {
+            if (winner != null && winner != currentBox) throw new IllegalGameStateException();
+            winner = currentBox;
+        }        currentBox = b.getBox(1, 3);
+        if (currentBox != null
+                && currentBox == b.getBox(2, 3)
+                && currentBox == b.getBox(3, 3)) {
+            if (winner != null && winner != currentBox) throw new IllegalGameStateException();
+            winner = currentBox;
+        }        return winner;
     }
 }
diff --git a/test/BoardTests.java b/test/BoardTests.java
index d6fdcf8..432399c 100644
--- a/test/BoardTests.java
+++ b/test/BoardTests.java
@@ -14,7 +14,7 @@ public class BoardTests {
         Random rng = RandomSingleton.get;
         int col = rng.nextInt();
         int row = rng.nextInt();
-        boolean shouldThrow = col >= 1 && col <= 3 && row >= 1 && row <= 3;
+        boolean shouldThrow = col < 1 || col > 3 || row < 1 || row > 3;
         return Stream.of(
                 Arguments.of(1, 1, false),
                 Arguments.of(1, 3, false),
diff --git a/test/InputCheckerTests.java b/test/InputCheckerTests.java
index abaa9df..1e524d0 100644
--- a/test/InputCheckerTests.java
+++ b/test/InputCheckerTests.java
@@ -6,7 +6,6 @@ import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.Arguments;
 import org.junit.jupiter.params.provider.MethodSource;
 
-import java.util.Random;
 import java.util.stream.Stream;
 
 public class InputCheckerTests {
@@ -15,7 +14,7 @@ public class InputCheckerTests {
         boolean isValid = val >= 1 && val <= 9;
         return Stream.of(
                 Arguments.of(1, true),
-                Arguments.of(1, true),
+                Arguments.of(9, true),
                 Arguments.of(-3, false),
                 Arguments.of(15, false),
                 Arguments.of(val, isValid)
diff --git a/test/WinCheckerTests.java b/test/WinCheckerTests.java
index 2a9bb0c..b6c5eb9 100644
--- a/test/WinCheckerTests.java
+++ b/test/WinCheckerTests.java
@@ -176,7 +176,7 @@ public class WinCheckerTests {
 
     @ParameterizedTest
     @MethodSource("getWinnerTestNormalData")
-    public void getWinnerTestNormal(Board b, Player expected){
+    public void getWinnerTestNormal(Board b, Player expected) throws IllegalGameStateException {
         Player actual = new WinChecker().getWinner(b);
         Assertions.assertEquals(expected, actual);
     }
@@ -194,7 +194,7 @@ public class WinCheckerTests {
     }
 
     @Test
-    public void getWinnerTestRandom(){
+    public void getWinnerTestRandom() throws IllegalGameStateException {
         Player currentBox;
         Board b = new Board();
         Player expected = null;