how to make a calculator 2

I want to add an exception handler to the calculator project for ZeroDivisionError_ in test_division

preview

Here 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 activate the virtual environment
```
source .venv/bin/activate
```
Attention

on Windows without Windows Subsystem for Linux use .venv/bin/activate.ps1 NOT source .venv/bin/activate
```
.venv/scripts/activate.ps1
```
the terminal shows
```
(.venv) .../pumping_python/calculator
```

I use pytest-watch to run the tests

pytest-watch

the terminal shows

rootdir: .../pumping_python/calculator
collected 4 items

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

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

I hold ctrl on the keyboard and 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_ in

    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 and exit the tests with ctrl+c on the keyboard, the terminal shows
```
(.venv) .../pumping_python/calculator
```
I deactivate the virtual environment
```
deactivate
```
the terminal goes back to the command line, (.venv) is no longer on the left side
```
.../pumping_python/calculator
```
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 the following

How many questions can you answer after going through this chapter?

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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