Project: Taxicab

Write a class called Taxicab with three private data members: the cab's x-coordinate, its y-coordinate, and its odometer reading.

The __init__ method takes two parameters, the starting x and y coordinates. It sets the odometer to zero.
There is a getter for each data member: get_x_coord, get_y_coord and get_odometer.
move_x takes a number saying how far the cab moves left or right.
move_y takes a number saying how far the cab moves up or down.
The odometer adds up the distance travelled, so moving left counts the same as moving right.

Here is how the class could be used:

cab = Taxicab(3, -8)       # creates a Taxicab object at coordinates (3, -8)
cab.move_x(4)              # moves cab 4 units "right"
cab.move_y(-5)             # moves cab 5 units "down"
cab.move_x(-2)             # moves cab 2 units "left"
print(cab.get_odometer())  # prints the current odometer reading

Save the file as Taxicab.py.

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Try the project on your own first. This is one working solution, followed by its tests. Press Run to run the tests. Read them to see what thorough testing looks like, then change the solution and run again to watch a test fail.

class Taxicab:
    """A taxicab that tracks its position and the distance it has driven."""

def __init__(self, x: int, y: int) -> None:
        """Place the cab at (x, y) with the odometer at zero."""
        self._x: int = x
        self._y: int = y
        self._odometer: int = 0

def get_x_coord(self) -> int:
        """Return the cab's x-coordinate."""
        return self._x

def get_y_coord(self) -> int:
        """Return the cab's y-coordinate."""
        return self._y

def get_odometer(self) -> int:
        """Return the total distance driven."""
        return self._odometer

def move_x(self, distance: int) -> None:
        """Move left or right. Any direction adds to the odometer."""
        self._x += distance
        self._odometer += abs(distance)

def move_y(self, distance: int) -> None:
        """Move up or down. Any direction adds to the odometer."""
        self._y += distance
        self._odometer += abs(distance)

# ---- Tests ----
import sys
import unittest

class TestTaxicab(unittest.TestCase):
    def setUp(self):
        self.cab = Taxicab(3, -8)

def test_a_new_cab_is_at_its_starting_coordinates(self):
        self.assertEqual(self.cab.get_x_coord(), 3)
        self.assertEqual(self.cab.get_y_coord(), -8)

def test_a_new_cab_has_an_odometer_of_zero(self):
        self.assertEqual(self.cab.get_odometer(), 0)

def test_moving_right_increases_x_and_leaves_y_alone(self):
        self.cab.move_x(4)
        self.assertEqual(self.cab.get_x_coord(), 7)
        self.assertEqual(self.cab.get_y_coord(), -8)

def test_moving_left_decreases_x(self):
        self.cab.move_x(-5)
        self.assertEqual(self.cab.get_x_coord(), -2)

def test_moving_up_increases_y_and_leaves_x_alone(self):
        self.cab.move_y(6)
        self.assertEqual(self.cab.get_y_coord(), -2)
        self.assertEqual(self.cab.get_x_coord(), 3)

def test_moving_down_decreases_y(self):
        self.cab.move_y(-5)
        self.assertEqual(self.cab.get_y_coord(), -13)

def test_moving_right_adds_to_the_odometer(self):
        self.cab.move_x(4)
        self.assertEqual(self.cab.get_odometer(), 4)

def test_moving_left_adds_to_the_odometer_too(self):
        self.cab.move_x(-4)
        self.assertEqual(self.cab.get_odometer(), 4)

def test_moving_up_adds_to_the_odometer(self):
        self.cab.move_y(6)
        self.assertEqual(self.cab.get_odometer(), 6)

def test_moving_down_adds_to_the_odometer_too(self):
        self.cab.move_y(-6)
        self.assertEqual(self.cab.get_odometer(), 6)

def test_moving_zero_changes_nothing(self):
        self.cab.move_x(0)
        self.cab.move_y(0)
        self.assertEqual(
            (self.cab.get_x_coord(), self.cab.get_y_coord(), self.cab.get_odometer()),
            (3, -8, 0),
        )

def test_the_example_from_the_project(self):
        self.cab.move_x(4)
        self.cab.move_y(-5)
        self.cab.move_x(-2)
        self.assertEqual(self.cab.get_odometer(), 11)
        self.assertEqual(self.cab.get_x_coord(), 5)
        self.assertEqual(self.cab.get_y_coord(), -13)

def test_the_move_methods_return_nothing(self):
        self.assertIsNone(self.cab.move_x(1))
        self.assertIsNone(self.cab.move_y(1))

def test_each_cab_keeps_its_own_state(self):
        other = Taxicab(0, 0)
        self.cab.move_x(5)
        self.assertEqual(other.get_x_coord(), 0)
        self.assertEqual(other.get_odometer(), 0)

# ---- Run the tests ----
loader = unittest.defaultTestLoader
suite = unittest.TestSuite(loader.loadTestsFromTestCase(case) for case in [TestTaxicab])
unittest.TextTestRunner(stream=sys.stdout, verbosity=2).run(suite)

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