Add unit tests for UnitFactory functionality and initialize units package

engine/unit_manager.py

@@ -0,0 +1,33 @@
+import random
+import uuid
+from units import rat, bomb
+
+class UnitManager:        
+    def count_rats(self):
+        count = 0
+        for unit in self.units.values():
+            if isinstance(unit, rat.Rat):
+                count += 1
+        return count
+            
+    def spawn_rat(self, position=None):
+        if position is None:
+            position = self.choose_start()
+        rat_class = rat.Male if random.random() < 0.5 else rat.Female
+        self.spawn_unit(rat_class, position)
+        
+    def spawn_bomb(self, position):
+        self.spawn_unit(bomb.Timer, position)
+
+    def spawn_unit(self, unit, position, **kwargs):
+        id = uuid.uuid4()
+        self.units[id] = unit(self, position, id, **kwargs)
+        
+    def choose_start(self):
+        if not hasattr(self, '_valid_positions'):
+            self._valid_positions = [
+                (x, y) for y in range(1, self.map.height-1) 
+                for x in range(1, self.map.width-1) 
+                if self.map.matrix[y][x]
+            ]
+        return random.choice(self._valid_positions)