rover: add backward method

rover/rover.py

@@ -20,15 +20,15 @@ class Rover(BaseModel):
     planet_size: Vector = Vector(x=100, y=100)
     dir: Direction = Direction.NORTH
 
-    def forward(self):
+    def _translate(self, value):
         if self.dir == Direction.NORTH:
-            self.pos.y += 1
+            self.pos.y += value
         elif self.dir == Direction.SOUTH:
-            self.pos.y -= 1
+            self.pos.y -= value
         elif self.dir == Direction.EAST:
-            self.pos.x += 1
+            self.pos.x += value
         elif self.dir == Direction.WEST:
-            self.pos.x -= 1
+            self.pos.x -= value
 
         if self.pos.x < 0:
             self.pos.x += self.planet_size.x
@@ -37,3 +37,9 @@ class Rover(BaseModel):
 
         self.pos.x %= self.planet_size.x
         self.pos.y %= self.planet_size.y
+
+    def forward(self):
+        self._translate(1)
+
+    def backward(self):
+        self._translate(-1)

rover/test_rover.py

@@ -92,3 +92,67 @@ def test_rover_can_wrap_over_east_west():
     )
     rov.forward()
     assert rov.pos == Vector(x=0, y=0)
+
+
+def test_rover_can_go_backward_north():
+    rov = Rover(
+        pos=Vector(x=0, y=1), planet_size=Vector(x=10, y=10), dir=Direction.NORTH
+    )
+    rov.backward()
+    assert rov.pos == Vector(x=0, y=0)
+
+
+def test_rover_can_go_backward_south():
+    rov = Rover(
+        pos=Vector(x=0, y=0), planet_size=Vector(x=10, y=10), dir=Direction.SOUTH
+    )
+    rov.backward()
+    assert rov.pos == Vector(x=0, y=1)
+
+
+def test_rover_can_go_backward_west():
+    rov = Rover(
+        pos=Vector(x=0, y=0), planet_size=Vector(x=10, y=10), dir=Direction.WEST
+    )
+    rov.backward()
+    assert rov.pos == Vector(x=1, y=0)
+
+
+def test_rover_can_go_backward_east():
+    rov = Rover(
+        pos=Vector(x=1, y=0), planet_size=Vector(x=10, y=10), dir=Direction.EAST
+    )
+    rov.backward()
+    assert rov.pos == Vector(x=0, y=0)
+
+
+def test_rover_can_go_backward_wrapping_under_north_south():
+    rov = Rover(
+        pos=Vector(x=0, y=0), planet_size=Vector(x=10, y=10), dir=Direction.NORTH
+    )
+    rov.backward()
+    assert rov.pos == Vector(x=0, y=9)
+
+
+def test_rover_can_go_backward_wrapping_over_north_south():
+    rov = Rover(
+        pos=Vector(x=0, y=9), planet_size=Vector(x=10, y=10), dir=Direction.SOUTH
+    )
+    rov.backward()
+    assert rov.pos == Vector(x=0, y=0)
+
+
+def test_rover_can_go_backward_wrapping_under_east_west():
+    rov = Rover(
+        pos=Vector(x=0, y=0), planet_size=Vector(x=10, y=10), dir=Direction.EAST
+    )
+    rov.backward()
+    assert rov.pos == Vector(x=9, y=0)
+
+
+def test_rover_can_go_backward_wrapping_over_east_west():
+    rov = Rover(
+        pos=Vector(x=9, y=0), planet_size=Vector(x=10, y=10), dir=Direction.WEST
+    )
+    rov.backward()
+    assert rov.pos == Vector(x=0, y=0)