Object oriented testing in Python

Last Updated : 01 Oct, 2020

Prerequisite: Object-Oriented Testing

Automated Object-Oriented Testing can be performed in Python using Pytest testing tool. In this article, we perform object-oriented testing by executing test cases for classes. We write a program that has one parent class called Product and three child classes - Snack, Beverage, and Staples. We implement all the classes and save them in a file called product.py. The classes have the following functions:

Snack - printDetails() and getExpDate()
Beverage - printDetails() and getExpDate()
Staples - printDetails() and getExpDate()

It is important to note that getExpDate() is an overridden function in this case.

Code in product.py file:

Python3

# importing the modules from datetime import date from dateutil.relativedelta import relativedelta  # base class   class Product:      name = ""      # printing the class in the constructor     def __init__(self):         print("super class Product")  # getExpDate() returns the expiry date of product # since every product has different expiry date # therefore this method is overridden by child classes     def getExpDate():          # gives exp date         print("Expiry date")         pass   # derived class 1 class Snack(Product):      # months     shelfLife = 6     price = 0      # constructor - initializing variables     def __init__(self, name, price):         self.name = name         self.price = price      # prints the Snack product details     def printDetails(self):         print("name : " + self.name)         print("price : " + str(self.price))         print("shelf life : " + str(self.shelfLife) + " months")      # calculates the expiry date using relativedelta library and returns     def getExpDate(self, pkdDate):         expDate = pkdDate + relativedelta(months=self.shelfLife)         return expDate  # derived class 2 class Beverage(Product):      # 2 years     shelfLife = 2     price = 0      # constructor - initializing variables     def __init__(self, name, price):         self.name = name         self.price = price      # prints the Beverage product details     def printDetails(self):         print("name : " + self.name)         print("price : " + str(self.price))         print("shelf life : " + str(self.shelfLife) + " years")      # calculates the expiry date using relativedelta      # library and returns     def getExpDate(self, pkdDate):         expDate = pkdDate + relativedelta(years=self.shelfLife)         return expDate   # derived class 3 class Staples(Product):      # 1 year     shelfLife = 1     price = 0      # constructor - initializing variables     def __init__(self, name, price):         self.name = name         self.price = price      # prints the Staples product details     def printDetails(self):         print("name : " + self.name)         print("price : " + str(self.price))         print("shelf life : " + str(self.shelfLife) + " year")      # calculates the expiry date using relativedelta     # library and returns     def getExpDate(self, pkdDate):         expDate = pkdDate + relativedelta(years=self.shelfLife)         return expDate   def main():     s = Snack('cookies', 60)     s.printDetails()     print(s.name + " will expire on " +           str(s.getExpDate(date(2019, 10, 3))) + "months")     # yyyy-mm-dd      p = Product()      st = Staples('rice', 300)     st.printDetails()     print(st.name + " will expire on " + str(st.getExpDate(date(2020, 1, 23))))      b = Beverage('coffee', 250)     b.printDetails()     print(b.name + " will expire on " + str(b.getExpDate(date(2018, 12, 17))))      print("done till here")   if __name__ == '__main__':     main()

Output:

name : cookies  price : 60  shelf life : 6 months  cookies will expire on 2020-04-03months  super class Product  name : rice  price : 300  shelf life : 1 year  rice will expire on 2021-01-23  name : coffee  price : 250  shelf life : 2 years  coffee will expire on 2020-12-17  done till here

To perform object-oriented testing, we write test cases for each of the classes. The following things should be kept in mind while writing these test cases:

Create a separate test class for testing the functions of each class, for e.g. TestSnack, TestStaple, TestBeverage
Write a test case for each function of a class
Use assert keyword to add assertions in the test cases. The assert statement will return True if the test case passes or will return False if the test case fails

We have written test cases for each function present in all classes of product.py file except the Product class (parent class). This is because the Product class has just one function and that too has been overridden by the child classes, so writing a test case would make no difference. Therefore, we write 6 test cases in total where two test cases are written for each of the child classes.

Code in test_product.py file:

Python3

# importing the modules import pytest from product import Snack, Staples, Beverage from datetime import date   class TestSnack:        # test case for print details of Snack     def test_details(self):         s = Snack('chips' , 50)         print("testing details : snack")         assert ('chips' , 50, 6)  == (s.name, s.price, s.shelfLife)      # test case for calculating exiry date of Snack     def test_expDate(self):         s = Snack('wafers', 40)         print("testing expiry date : snack")         expdate = s.getExpDate(date(2019, 10, 3))         assert expdate == date(2020, 4, 3)   class TestStaple:        # test case for print details of Staples     def test_details(self):         st = Staples('rice' , 300)         print("testing details : staples")         assert ('rice' , 300, 1)  == (st.name, st.price, st.shelfLife)      # test case for calculating exiry date of Staples     def test_expDate(self):         st = Staples('wheat flour', 400)         print("testing expiry date : staples")         expdate = st.getExpDate(date(2020, 1, 23))         assert expdate == date(2021, 1, 23)    class TestBeverage:        # test case for print details of Beverage     def test_details(self):         b = Beverage('coffee' , 250)         print("testing details : beverage")         assert ('coffee' , 250, 2)  == (b.name, b.price, b.shelfLife)      # test case for calculating exiry date of Beverage     def test_expDate(self):         b = Beverage('green tea', 400)         print("testing expiry date : beverage")         expdate = b.getExpDate(date(2018, 12, 17))         assert expdate == date(2020, 12, 17)

Note: The function name and the test file name should always start with the word 'test'.

To execute the above test cases, create two separate files, product.py and test_product.py in a single folder. To execute write the following command: