how to make a calculator 2

I want to use assertRaises to make sure test_division from the calculator project raises ZeroDivisionError

preview

These are the tests I have by the end of the chapter

import random
import src.calculator
import unittest


def a_random_number():
    return random.triangular(-1000.0, 1000.0)


class TestCalculator(unittest.TestCase):

    random_first_number = a_random_number()
    random_second_number = a_random_number()

    def test_addition(self):
        self.assertEqual(
            src.calculator.add(
                self.random_first_number,
                self.random_second_number
            ),
            self.random_first_number+self.random_second_number
        )

    def test_subtraction(self):
        self.assertEqual(
            src.calculator.subtract(
                self.random_first_number,
                self.random_second_number
            ),
            self.random_first_number-self.random_second_number
        )

    def test_multiplication(self):
        self.assertEqual(
            src.calculator.multiply(
                self.random_first_number,
                self.random_second_number
            ),
            self.random_first_number*self.random_second_number
        )

    def test_division(self):
        self.assertEqual(
            src.calculator.divide(
                self.random_first_number,
                self.random_second_number
            ),
            self.random_first_number/self.random_second_number
        )
        with self.assertRaises(ZeroDivisionError):
            src.calculator.divide(self.random_first_number, 0)


# Exceptions seen
# AssertionError
# NameError
# AttributeError
# TypeError

open the project

I change directory to the calculator folder
```
cd calculator
```
the terminal shows I am in the calculator folder
```
.../pumping_python/calculator
```

I use pytest-watcher to run the tests

uv run pytest-watcher . --now

the terminal shows

rootdir: .../pumping_python/calculator
configfile: pyproject.toml
collected 4 items

tests/test_calculator.py ....                                 [100%]

======================== 4 passed in X.YZs =========================

I hold ctrl on the keyboard, then click on tests/test_calculator.py to open it in the editor

test catching ZeroDivisionError in test_calculator.py

RED: make it fail

I add a new assertion to show that the divide function raises ZeroDivisionError when I try to divide a number by 0

    def test_division(self):
        self.assertEqual(
            src.calculator.divide(
                self.random_first_number,
                self.random_second_number
            ),
            self.random_first_number/self.random_second_number
        )
        src.calculator.divide(self.random_first_number, 0)


# Exceptions seen

the terminal shows ZeroDivisionError

ZeroDivisionError: float division by zero

GREEN: make it pass

I add assertRaises

            self.random_first_number/self.random_second_number
        )
        with self.assertRaises(ZeroDivisionError):
            src.calculator.divide(self.random_first_number, 0)


# Exceptions seen

the test passes

close the project

I close test_calculator.py in the editor
I click in the terminal, then use q on the keyboard to leave the tests. The terminal goes back to the command line
I change directory to the parent of calculator
```
cd ..
```
the terminal shows
```
.../pumping_python
```
I am back in the pumping_python directory

review

I can use assertRaises to catch Exceptions in tests and tested these

code from the chapter

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

what is next?

you know

Would you like to test handling Exceptions in programs?

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