I used these slides when delivering a meetup about Unit Testing in Python. You can find the video at https://youtu.be/5QHArdkUeYc

1. Unit Testing in Python
Haim Michael
August 1st
, 2022
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2. © 2008 Haim Michael 20150805
What is Unit Testing?

3. © 2008 Haim Michael 20150805
What is Unit Testing?
 Unit test is a way of testing a unit (the smallest piece of code
that can be logically isolated in a system). In most
programming languages, that is a function, a subroutine, a
method or a property.

4. © 2008 Haim Michael 20150805
The TDD Methodology
 Test Driven Development (TDD) is a software development
methodology that focuses on creating unit test cases before
developing the actual code.

5. © 2008 Haim Michael 20150805
The TDD Methodology
 TDD leads to repetitive work flow in which we write the test,
write the code to be tested, execute the test and repeat these
two steps till the test passes.
Image Credit: TutorialPoint.com

6. © 2008 Haim Michael 20150805
The pytest Framework

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The pytest Framework
 The pytest framework assists us with the development of
small readable tests. In addition, we can also use this library
when developing complex functional tests.
https://pytest.org

8. © 2008 Haim Michael 20150805
Installing The pytest Framework
 We can easily install this framework using the pip utility.
pip install -U pytest
 We can easily check the version of the pytest library we have
just installed using the following command:
pytest --version
Upgrading to Newest Version

9. © 2008 Haim Michael 20150805
Using The pytest Framework
 We can easily use the pytest framework by executing the
utility. Doing so, all files of the form test_*.py or
_test.py in the current directory and its subdirectories will
be examined, and all tests (functions their names start with
test_) will be called.
pytest

10. © 2008 Haim Michael 20150805
Simple Code Sample
def total(num1: int, num2: int) -> int:
result = num1 + num2
return result
def multiply(num1: int, num2: int) -> int:
result = num1 * num2
return result
utils.py

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Simple Code Sample
import utils
def test_total():
actual_value = utils.total(3, 5)
expected_value = 8
assert actual_value == expected_value
def test_multiply():
actual_value = utils.multiply(3, 5)
expected_value = 15
assert actual_value == expected_value
test_utils.py

12. © 2008 Haim Michael 20150805
Simple Code Sample

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Grouping Multiple Tests in Class
 We can group our tests in a class. We just need to define
each and every function with a name that starts with test_.
 There is no need to define a class that extends a specific
class that already exists. We just need to make sure that the
name of our class starts with Test.

14. © 2008 Haim Michael 20150805
Simple Code Sample
class BankAccount:
def __init__(self,id,balance):
self.id = id
self.balance = balance
def deposit(self,sum):
self.balance += sum
def withdraw(self,sum):
self.balance -= sum
banking.py

15. © 2008 Haim Michael 20150805
Simple Code Sample
import banking
class TestBankAccount:
def test_deposit(self):
ob = banking.BankAccount(123123,1000)
ob.deposit(80)
ob.deposit(120)
ob.deposit(400)
assert ob.balance == 1600
def test_withdraw(self):
ob = banking.BankAccount(123123,1000)
ob.withdraw(80)
ob.withdraw(120)
ob.withdraw(400)
assert ob.balance == 400
test_banking.py

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Simple Code Sample

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Assert Exceptions Raising
 We can assert whether a specific function raised an exception
using the raises helper.

18. © 2008 Haim Michael 20150805
Simple Code Sample
class BankAccount:
def __init__(self, id, balance):
self.id = id
self.balance = balance
def deposit(self, sum):
self.balance += sum
def withdraw(self, sum):
if sum<self.balance:
self.balance -= sum
else:
raise BankException("balance cannot be negative")
class BankException(Exception):
def __init__(self, message):
super().__init__(self, message)
banking.py

19. © 2008 Haim Michael 20150805
Simple Code Sample
import banking
import pytest
class TestBankAccount:
def perform_withdraws(self):
ob = banking.BankAccount(123123, 100)
ob.withdraw(80)
ob.withdraw(10)
ob.withdraw(30)
def test_withdraw(self):
with pytest.raises(banking.BankException):
self.perform_withdraws()
test_banking.py

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Simple Code Sample

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The requests Library

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The Requests Library
 Requests is a simple HTTP library for Python. It allows us to
send HTTP requests.
https://docs.python-requests.org

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Installation of Requests
 We can easily install Requests by using the pip command:
pip install requests

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The GET Request
 We can easily initiate a GET request by calling the
requests.get() method.

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The GET Request
import requests
data = requests.get("https://api.coinbase.com/v2/currencies")
print(data.status_code)
print(data.content)
print(data.text)
print(data.json()) #dict object
print(data.headers) #dict object

26. © 2008 Haim Michael 20150805
The GET Request

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Query String Parameters
 We can easily customize the GET request, and send query
string parameters in the URL, by passing over a reference for
a dict object that holds those parameters.

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Query String Parameters
import requests
response = requests.get(
"https://api.github.com/search/repositories",
params={'q': 'requests+language:python'})
data = response.json()
print(data)

29. © 2008 Haim Michael 20150805
Request Headers
 We can easily customize the headers that are sent together
with the request by passing over a reference for a dict object
that holds the headers we want to customize. The names of
the headers are the keys, and the values of the headers are
the values of those keys.

30. © 2008 Haim Michael 20150805
Request Headers
import requests
response = requests.get(
"https://api.github.com/search/repositories",
params={'q': 'requests+language:python'},
headers={'sec-ch-ua-platform': 'macOS'})
data = response.json()
print(data)

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Other HTTP Methods
 In addition to the get() method, The Requests library
provides us with other similar methods for each one of the
other HTTP methods.

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Other HTTP Methods
import requests
response = requests.post('https://httpbin.org/post',
data={'key':'value'})
print(response.json())
response = requests.put('https://httpbin.org/put',
data={'key':'value'})
print(response.json())
response = requests.delete('https://httpbin.org/delete')
print(response.json())

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Other HTTP Methods

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Introspecting The Request
 When making the request, the Requests library prepares the
request before sending it.
 We can introspect the request by referring the request
attribute of the response object.

35. © 2008 Haim Michael 20150805
Introspecting The Request
import requests
response = requests.post('https://httpbin.org/post', data={'key':'value'})
print(response.request.headers['Content-Type'])
print(response.request.url)
print(response.request.body)

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REStful Web Services Testing
 We can easily write unit tests for REStful web services using
the PyTest unit testing framework and the Requests library.

37. © 2008 Haim Michael 20150805
REStful Web Services Testing
import requests
def test_get_status_code_ok_from_httpbin():
response = requests.get(
'https://httpbin.org/get',
data={'key': 'value'})
assert response.status_code == 200

38. © 2008 Haim Michael 20150805
Best Practices

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Readable Code
 The unit tests we develop should be updated in accordance
with the changes that take place in the code we test.
 Having readable code will eases the update of the unit tests
code, either by us or by others.

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Deterministic Tests
 It would be better if we use deterministic data instead of
randomized generated one.
 Deterministic tests either pass in all executions or not. They
exhibit the same behavior every time they run.

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Avoid Interdependencies
 We better have each test case with its own setup and
teardown mechanism in order to avoid interdependencies
between the tests.

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Avoid Logic
 Writing unit tests with logical conditions, manual strings
concatenation and various calculations might increase the
risk for bugs in our unit tests. The tests should focus on the
expected result.

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Implementing TDD
 When we develop our unit tests before we develop the code
the quality of our tests improves.

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CI/CD Integration
 Integrating our unit tests into the CI/CD pipeline will allow us
to run them several times per day (automatically). Doing so
will improve the quality of our code.

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Update Our Tests
 Maintaining and updating the tests periodically will improve
their quality.

46. © 2009 Haim Michael All Rights Reserved 46
Questions & Answers
Thanks for Your Time!
Haim Michael
haim.michael@lifemichael.com
+972+3+3726013 ext:700
+972+54+6655837 (whatsapp)
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