rover: define default values for Rover fields

rover/rover.py

@@ -9,5 +9,5 @@ class Vector:
 
 @dataclass
 class Rover:
-    pos: Vector
-    planet_size: Vector
+    pos: Vector = (0, 0)
+    planet_size: Vector = (100, 100)

rover/test_rover.py

@@ -4,3 +4,8 @@ from rover import Rover
 def test_rover_constructor():
     rov = Rover(pos=(0, 0), planet_size=(100, 100))
     assert rov.pos == (0, 0) and rov.planet_size == (100, 100)
+
+
+def test_rover_default_values():
+    rov = Rover()
+    assert rov.pos == (0, 0) and rov.planet_size == (100, 100)