rover: add non-negative coordinate validation

rover/rover.py

@@ -2,13 +2,25 @@ import enum
 from copy import deepcopy
 from typing import List
 
-from pydantic import BaseModel
+from pydantic import BaseModel, validator
 
 
 class Vector(BaseModel):
     x: int = 0
     y: int = 0
 
+    @validator("x")
+    def _x_must_be_positive(x):
+        if x < 0:
+            raise ValueError("x must be positive")
+        return x
+
+    @validator("y")
+    def _y_must_be_positive(y):
+        if y < 0:
+            raise ValueError("y must be positive")
+        return y
+
 
 class Direction(enum.Enum):
     NORTH = "N"

rover/test_rover.py

@@ -1,4 +1,6 @@
 import pytest
+from pydantic import ValidationError
+
 from rover import Commander, Direction, ObstacleError, Rover, Vector
 
 
@@ -225,3 +227,13 @@ def test_commander_command_with_obstacles():
     with pytest.raises(ObstacleError):
         com.parse_execute("FFRF")
     assert com.rover == Rover(pos=Vector(x=0, y=2), dir=Direction.EAST)
+
+
+def test_rover_negative_x_construction():
+    with pytest.raises(ValidationError):
+        _ = Rover(pos=Vector(x=-1, y=0))
+
+
+def test_rover_negative_y_construction():
+    with pytest.raises(ValidationError):
+        _ = Rover(pos=Vector(x=0, y=-1))