diff --git a/Game/gamestate.py b/Game/gamestate.py
index 734f737..9c7b41b 100644
--- a/Game/gamestate.py
+++ b/Game/gamestate.py
@@ -19,7 +19,7 @@ class GameState:
 
     _playfield: list[list[int]]
     _finished: bool
-    _winner: int
+    _winner: int = None
 
     def __init__(self, playfiled_dimensions: tuple[int, int] = (3,3)):
         """
@@ -93,3 +93,13 @@ def playfield_value(self, position: tuple[int, int]) -> int:
             int: The value at the specified position on the playfield.
         """
         return self._playfield[position[0]][position[1]]
+
+    @property
+    def playfield_dimensions(self) -> tuple[int, int]:
+        """
+        Returns the size of the playfield.
+
+        Returns:
+            tuple[int, int]: The size of the playfield.
+        """
+        return (len(self._playfield), len(self._playfield[0]))
diff --git a/Game/rulebase.py b/Game/rulebase.py
index efdade3..a9e324b 100644
--- a/Game/rulebase.py
+++ b/Game/rulebase.py
@@ -72,14 +72,18 @@ def check_win(self, state: GameState):
                 return
 
         # Check vertical lines
-        for column in state.playfield.T:
+        for column in transpose(state.playfield):
             if len(set(column)) == 1 and column[0] != 0:
                 state.set_winner(column[0])
                 return
 
         # Check diagonals
-        diagonal1 = [state.playfield[i][i] for i in range(min(state.playfield_dimensions))]
-        diagonal2 = [state.playfield[i][j] for i, j in zip(range(min(state.playfield_dimensions)), range(max(state.playfield_dimensions)-1, -1, -1))]
+        if state.playfield_dimensions[0] != state.playfield_dimensions[1]:
+            # playfield is not square and thus has no diagonal winning condition
+            return
+
+        diagonal1 = [state.playfield[i][i] for i in range(state.playfield_dimensions[0])]
+        diagonal2 = [state.playfield[i][j] for i in range(state.playfield_dimensions[0]) for j in range(state.playfield_dimensions[0], -1)]
         if len(set(diagonal1)) == 1 and diagonal1[0] != 0:
             state.set_winner(diagonal1[0])
             return
@@ -91,7 +95,7 @@ def check_win(self, state: GameState):
             state.set_winner(0)
             return
 
-        return 0
+        return
 
     def is_game_state_valid(self, state: GameState) -> bool:
         """
@@ -122,3 +126,16 @@ def explain(self, state: GameState, prev: tuple[int, int], new: tuple[int, int])
 
         """
         return ""  # TODO
+
+def transpose(matrix: list[list[int]]) -> list[list[int]]:
+    """
+    Transpose a matrix.
+
+    Args:
+        matrix (list[list[int]]): The matrix to transpose.
+
+    Returns:
+        list[list[int]]: The transposed matrix.
+
+    """
+    return [list(row) for row in zip(*matrix)]
diff --git a/Game/test_rulebase.py b/Game/test_rulebase.py
new file mode 100644
index 0000000..ae1357a
--- /dev/null
+++ b/Game/test_rulebase.py
@@ -0,0 +1,73 @@
+from gamestate import GameState
+from rulebase import RuleBase
+
+def test_is_move_valid():
+    # Create a GameState object
+    state = GameState()
+
+    # Create a RuleBase object
+    rulebase = RuleBase()
+
+    # Test case 1: Valid move
+    new_position = (0, 0)
+    assert rulebase.is_move_valid(state, new_position) == True
+
+    # Test case 2: Invalid move (position already occupied)
+    state.set_player_position(1, new_position)
+    assert rulebase.is_move_valid(state, new_position) == False
+
+def test_check_win():
+
+    # Test case 1: No winner
+    state = GameState()
+    rulebase = RuleBase()
+    rulebase.check_win(state)
+    assert state.winner == 0 & state.finished == False
+
+    # Test case 2: Horizontal win
+    state = GameState()
+    rulebase = RuleBase()
+    state._playfield = [[1, 1, 1], [0, 2, 0], [2, 0, 2]]
+    rulebase.check_win(state)
+    assert state.winner == 1 & state.finished == True
+
+    # Test case 3: Vertical win
+    state = GameState()
+    rulebase = RuleBase()
+    state._playfield = [[1, 0, 2], [1, 0, 2], [1, 2, 0]]
+    rulebase.check_win(state)
+    assert state.winner == 1 & state.finished == True
+
+    # Test case 4: Diagonal win
+    state = GameState()
+    rulebase = RuleBase()
+    state._playfield = [[1, 0, 2], [2, 1, 0], [2, 0, 1]]
+    rulebase.check_win(state)
+    assert state.winner == 1 & state.finished == True
+
+    # Test case 5: Draw
+    state = GameState()
+    rulebase = RuleBase()
+    state._playfield = [[1, 2, 1], [1, 2, 2], [2, 1, 1]]
+    rulebase.check_win(state)
+    assert state.winner == 0 and state.finished == True
+
+def test_is_game_state_valid():
+    # Create a GameState object
+    state = GameState()
+
+    # Create a RuleBase object
+    rulebase = RuleBase()
+
+    # Test case 1: Valid game state
+    assert rulebase.is_game_state_valid(state) == True
+
+    # Test case 2: Invalid game state (difference in player counts > 1)
+    state.set_player_position(1, (0, 0))
+    state.set_player_position(1, (0, 1))
+    assert rulebase.is_game_state_valid(state) == False
+
+# Run the test cases
+test_is_move_valid()
+test_check_win()
+test_is_game_state_valid()