Christian Shadis

CS-443 Self-Directed Blog Post #5

This past semester I have been spending a lot of time in my QA class working with JUnit 5. I want to be able to take my familiarity with JUnit and apply the same principles with unit testing in Python. I am leaning toward a data-centric career path and Python is widely used for data analytics, so this would be valuable information for me.

This post is not an expert-authored tutorial on Python unit testing because I, myself, am just getting started with it. In this post I will instead give tiny, bite-sized examples of just the basics, translating it from JUnit to Python unittest. I built identical, small classes in Java and Python, and will build tests to go with them. Below are the classes in Java and Python, respectively.

/**
 * Simple class with basic methods, written in Java
 * @author Christian Shadis
 */
public class main {
    public static void main(String[] args){
        int i = 0; // dummy code to keep compiler happy
    }

    public static int addTwoNumbers(int x, int y){
        return x + y;
    }

    public static String toCapital(String str){
        return str.toUpperCase();
    }
}

# Simple class with basic functions, written in Python
# Author: Christian Shadis

class main:
    def add_two_numbers(x, y):
        return x+y

    def to_capital(string):
        return string.upper()

Writing the unit tests in JUnit is simple: we import the JUnit assertions, and the @Test annotation. Then we create the test class, each of the two tests, setup, exercise, and verify just as always.

/**
 * Test Class for main.java
 * @author: Christian Shadis
 */
import static org.junit.jupiter.api.Assertions.*;
import org.junit.jupiter.api.Test;

public class maintest {

    @Test
    void testAddTwoNumbers(){
        int result; // setup
        result = main.addTwoNumbers(566, 42); // exercise
        assertEquals(result, 608); // verify
    }

    @Test
    void testToCapital(){
        String result; // setup
        result = main.toCapital("string"); // exercise
        assertEquals(result, "STRING"); // verify
    }
}

Luckily, writing unit tests is just as easy in Python as Java. We import the unittest library and the other class, define the class, and add a Test Case object as the parameter.

import unittest
from main import *

class maintest(unittest.TestCase):
import unittest
from main import *

class maintest(unittest.TestCase):

    def test_add_two_numbers(self):

        pass
    def test_to_capital(self):

        pass

Now we need a test case for each of our two functions, add_two_numbers and to_capital. Python’s unittest objects have very similar assertions as in JUnit. Use assertEqual(x, y) to check that x == y. This is the assertion we will use in this example, but any of the following are commonly used unittest assertions:

• assertEqual
• assertNotEqual
• assertTrue
• assertFalse
• assertIs
• assertIsNot
• assertIsNone
• assertIsNotNone
• assertIn
• assertNotIn
• assertIsInstance
• assertIsNotInstance

assertEqual takes two arguments and, as the name suggests, asserts their equality. See the implementation below:

    def test_add_two_numbers(self):
        result = main.add_two_numbers(33, 44)
        self.assertEqual(result, 77)

    def test_to_capital(self):
        result = main.to_capital("hi")
        self.assertEqual(result, "HI")

Run the tests and you will see them both pass. Below is a screenshot of the tests executing in Python and then in JUnit. As you can see, the Python tests are slightly faster than the Java tests, but not by much. I used IntelliJ IDEA and Pycharm IDE.

I have found the most helpful way to learn testing is to just play around with the unit tests, see what works and what doesn’t, see what causes failures and what those failures look like, and so forth. I would suggest any other beginner QA student to do the same. Playing around with different assertions and looking at the unittest documentation is a great way to learn this library. I hope this post gave you some insight on how to get started with unit testing your Python modules if you have done some work with JUnit in the past.

4/28/2021

Works Cited:
Unittest – unit testing framework¶. (n.d.). Retrieved April 28, 2021, from https://docs.python.org/3/library/unittest.html

From the blog CS@Worcester – Christian Shadis' Blog by ctshadis and used with permission of the author. All other rights reserved by the author.