test car with list comprehensions

I want to use for loops in the Car project. It has tests for a Car ignition with these inputs:

was the start button pressed?
is the key close to the ignition?
is the brake being pressed?
is the car in park?

the inputs gave me this truth table

key	brake	start	gear	output
close	pressed	pressed	in park	True
close	pressed	pressed	NOT in park	False
close	NOT pressed	pressed	in park	False
close	NOT pressed	pressed	NOT in park	False

key	brake	start	gear	output
NOT close	pressed	pressed	in park	False
NOT close	pressed	pressed	NOT in park	False
NOT close	NOT pressed	pressed	in park	False
NOT close	NOT pressed	pressed	NOT in park	False

key	brake	start	gear	output
close	pressed	NOT pressed	in park	False
close	pressed	NOT pressed	NOT in park	False
close	NOT pressed	NOT pressed	in park	False
close	NOT pressed	NOT pressed	NOT in park	False

key	brake	start	gear	output
NOT close	pressed	NOT pressed	in park	False
NOT close	pressed	NOT pressed	NOT in park	False
NOT close	NOT pressed	NOT pressed	in park	False
NOT close	NOT pressed	NOT pressed	NOT in park	False

the only time the Car starts is if the start button is pressed AND the key is close to the ignition AND the brake is being pressed AND the car gear is in park.

preview

This is the test I have at the end of the chapter

car/tests/test_car_w_loops.py

import src.car
import unittest


class TestCar(unittest.TestCase):

    def test_car_ignition(self):
        booleans = (False, True)
        for start_is_pressed in booleans:
            for key_is_close in booleans:
              for brake_is_pressed in booleans:
                  for in_park in booleans:
                      with self.subTest(
                          start_is_pressed=start_is_pressed,
                          key_is_close=key_is_close,
                          brake_is_pressed=brake_is_pressed,
                          in_park=in_park,
                      ):
                          result = src.car.ignition(
                              start_is_pressed=start_is_pressed,
                              key_is_close=key_is_close,
                              brake_is_pressed=brake_is_pressed,
                              in_park=in_park,
                          )
                          try:
                              self.assertFalse(result)
                          except AssertionError:
                              self.assertTrue(result)


# Exceptions seen
# AssertionError
# NameError
# AttributeError
# TypeError
# SyntaxError

open the project

I open a terminal
I change directory to the car folder in the pumping_python folder
terminal
```
cd car
```
I open test_car.py from the tests folder
I use pytest-watcher to run the tests automatically
terminal
```
uv run pytest-watcher . --now
```

extract test_car_ignition

RED: make it fail

I add a test with a for loop for all the cases

car/tests/test_car.py

class TestCar(unittest.TestCase):

    def test_car_ignition(self):
        booleans = (False, True)
        for start_is_pressed in booleans:
            for key_is_close in booleans:
              for brake_is_pressed in booleans:
                  for in_park in booleans:
                      with self.subTest(
                          start_is_pressed=start_is_pressed,
                          key_is_close=key_is_close,
                          brake_is_pressed=brake_is_pressed,
                          in_park=in_park,
                      ):

car/tests/test_car.py

                          result = src.car.ignition(
                              start_is_pressed=start_is_pressed,
                              key_is_close=key_is_close,
                              brake_is_pressed=brake_is_pressed,
                              in_park=in_park,
                          )
                          self.assertEqual(result, 'BOOM!!!')

    def test_park_w_brake_pressed_key_close_start_pressed(self):

the terminal is my friend, and shows AssertionError

terminal

SUBFAILED(
    start_is_pressed=False, key_is_close=False,
    brake_is_pressed=False, in_park=False
) ... AssertionError: False != 'BOOM!!!'
SUBFAILED(
    start_is_pressed=False, key_is_close=False,
    brake_is_pressed=False, in_park=True
) ... AssertionError: False != 'BOOM!!!'
SUBFAILED(
    start_is_pressed=False, key_is_close=False,
    brake_is_pressed=True, in_park=False
) ... AssertionError: False != 'BOOM!!!'
SUBFAILED(
    start_is_pressed=False, key_is_close=False,
    brake_is_pressed=True, in_park=True
) ... AssertionError: False != 'BOOM!!!'

terminal

SUBFAILED(
    start_is_pressed=False, key_is_close=True,
    brake_is_pressed=False, in_park=False
) ... AssertionError: False != 'BOOM!!!'
SUBFAILED(
    start_is_pressed=False, key_is_close=True,
    brake_is_pressed=False, in_park=True
) ... AssertionError: False != 'BOOM!!!'
SUBFAILED(
    start_is_pressed=False, key_is_close=True,
    brake_is_pressed=True, in_park=False
) ... AssertionError: False != 'BOOM!!!'
SUBFAILED(
    start_is_pressed=False, key_is_close=True,
    brake_is_pressed=True, in_park=True
) ... AssertionError: False != 'BOOM!!!'

terminal

SUBFAILED(
    start_is_pressed=True, key_is_close=False,
    brake_is_pressed=False, in_park=False
) ... AssertionError: False != 'BOOM!!!'
SUBFAILED(
    start_is_pressed=True, key_is_close=False,
    brake_is_pressed=False, in_park=True
) ... AssertionError: False != 'BOOM!!!'
SUBFAILED(
    start_is_pressed=True, key_is_close=False,
    brake_is_pressed=True, in_park=False
) ... AssertionError: False != 'BOOM!!!'
SUBFAILED(
    start_is_pressed=True, key_is_close=False,
    brake_is_pressed=True, in_park=True
) ... AssertionError: False != 'BOOM!!!'

terminal

SUBFAILED(
    start_is_pressed=True, key_is_close=True,
    brake_is_pressed=False, in_park=False
) ... AssertionError: False != 'BOOM!!!'
SUBFAILED(
    start_is_pressed=True, key_is_close=True,
    brake_is_pressed=False, in_park=True
) ... AssertionError: False != 'BOOM!!!'
SUBFAILED(
    start_is_pressed=True, key_is_close=True,
    brake_is_pressed=True, in_park=False
) ... AssertionError: False != 'BOOM!!!'
SUBFAILED(
    start_is_pressed=True, key_is_close=True,
    brake_is_pressed=True, in_park=True
) ... AssertionError: True != 'BOOM!!!'

GREEN: make it pass

I change self.assertEqual(result, 'BOOM!!!') to handle the fifteen cases where the ignition function returns False

car/tests/test_car.py

                          result = src.car.ignition(
                              start_is_pressed=start_is_pressed,
                              key_is_close=key_is_close,
                              brake_is_pressed=brake_is_pressed,
                              in_park=in_park,
                          )
                          self.assertFalse(result)

    def test_park_w_brake_pressed_key_close_start_pressed(self):

the terminal is my friend, and shows AssertionError for the one case where the Car starts.

terminal

SUBFAILED(
    start_is_pressed=True, key_is_close=True,
    brake_is_pressed=True, in_park=True
) ... AssertionError: True is not false

I move the assertion into a try statement for it

car/tests/test_car.py

                          result = src.car.ignition(
                              start_is_pressed=start_is_pressed,
                              key_is_close=key_is_close,
                              brake_is_pressed=brake_is_pressed,
                              in_park=in_park,
                          )
                          try:
                              self.assertFalse(result)
                          except AssertionError:
                              self.assertTrue(result)

    def test_park_w_brake_pressed_key_close_start_pressed(self):

the test passes.

REFACTOR: make it better

I remove all the other tests because they are now covered by test_car_ignition

car/tests/test_car.py

                          try:
                              self.assertFalse(result)
                          except AssertionError:
                              self.assertTrue(result)


# Exceptions seen

I add a git commit message in the other terminal
terminal
```
git commit -am \
'extract test_car_ignition'
```

close the project

I close tests/test_car.py
I click in the terminal where the tests are running
I use q on the keyboard to leave the tests
I change directory to the parent of Car
terminal
```
cd ..
```

review

Once again, I used four nested for loops (ugly) to put all the tests together which leaves me with less lines of code and something that is harder to understand.

There has to be a better way that does not write this many loops.

code from the chapter

Do you want to see all the CODE I typed in this chapter?

what is next?

Would you like to test making an Elevator?

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