Understanding Unit Testing in Python: Testing Laundry Price Calculations

What is Unit Testing?

In the world of software development, ensuring that your code works correctly is crucial. This is where unit testing comes into play. Unit testing is a type of software testing where individual units or components of the software are tested. The primary goal is to validate that each unit of the software performs as expected.

Unit testing helps developers identify and fix bugs early in the development process, which can save time and reduce costs. Additionally, it makes the codebase more maintainable and reliable, leading to higher-quality software.

In this article, we'll explore the basics of unit testing in Python using the unittest library. To make it more practical, we'll walk through a real-world example: testing the calculation of laundry prices. This project involves creating a function to calculate the total cost of laundry based on the weight of the clothes and the price per kilogram. By the end of this article, you’ll have a solid understanding of how to implement and run unit tests in Python, ensuring your functions work correctly and efficiently.

About Laundry Price Calculations

In our daily lives, many of us rely on laundry services to save time and effort. Typically, the cost of these services is calculated based on the weight of the clothes and a fixed price per kilogram. To automate and simplify this calculation, we can write a Python function that takes the weight of the laundry and the price per kilogram as inputs and returns the total cost.

This project aims to create a reliable function for calculating laundry prices and ensure its accuracy through unit testing. By doing so, we can avoid potential errors and guarantee consistent results, which is especially important for businesses relying on precise cost calculations.

Business Rules

As a business in general, of course, laundry seeks profit. In this project, we will define some business rules to get closer to what happens in the real world.

1. Minimum order is 3kg.

2. Orders under 3kg will be counted as a minimum order (3kg).

3. Only Complete Express and Speedy Express packages are available for orders under or equal to 1 day.

There will be 4 packages:

No need to be confused for packages with the same name, they are still the same package, it's just that the price and duration of work are different.

The Logic

The logic is quite simple, the program calculates the total price to be paid based on the quantity of laundry (kg) and the price of the laundry package.

Example

Now it's Time to Code

1. Setting Up the Environment

   • Ensure you have Python installed from python.org.

   • Use an IDE like PyCharm or VS Code for coding.

2. hargaBayar.py

   Create a file with name hargaBayar.py.

   Here is the code for the class that calculates laundry prices:

    """
    Description
    mko = Minimum Kilogram
    prk = Price Per Kilogram
    dy = Day
    tpy = Total Pay
    pkg = Package
    desc = Package Name
   
    Package options:
    1. Folded Dry Cleaning
    2. Iron Dry Cleaning
    3. Complete Express
    4. Speedy Express
    """
   
    class calcPayment:
        def __init__(self, pkg, ko, dy):
            self.pkg = pkg
            self.ko = ko
            self.dy = dy
            self.desc = None
   
        def countTotal(self):
            mko = 3.00
            prk = 0.00
            tpy = 0.00
   
            ## Package calculations (1) Folded Dry Cleaning
            if self.pkg == 1:
                self.desc = "Folded Dry Cleaning"
                prk = 7000.00
   
                if self.dy < 3:
                    if self.dy > 1:
                        prk = 8500.00
                        if self.ko < mko:
                            self.ko = mko
                    elif self.dy < 2:
                        raise ValueError("Folded Dry Cleaning at the earliest 2 days")
                else:
                    if self.ko <= 3:
                        self.ko = mko
   
                tpy = prk * self.ko
   
            ## Package calculations (2) Iron Dry Cleaning
            elif self.pkg == 2:
                self.desc = "Iron Dry Cleaning"
                prk = 10000.00
   
                if self.dy < 3:
                    if self.dy > 1:
                        prk = 12000.00
                        if self.ko < mko:
                            self.ko = mko
                    elif self.dy < 2:
                        raise ValueError("Iron Dry Cleaning at the earliest 2 days")
                else:
                    if self.ko <= 3:
                        self.ko = mko
   
                tpy = prk * self.ko
   
            ## Package calculations (3) Complete Express in 1 day
            elif self.pkg == 3:
                self.desc = "Complete Express"
                self.dy = 1
                prk = 15000.00
   
                if self.ko < mko:
                    self.ko = mko
   
                tpy = prk * self.ko
   
            ## Package calculations (4) Speedy Express in 5 hours
            elif self.pkg == 4:
                self.desc = "Speedy Express"
                prk = 25000.00
                self.dy = 0.2083
   
                tpy = prk * self.ko
   
            print("Note:")
            print("1. Orders under 3 kilograms will be counted as a minimum order (3kg).")
            print(
                "2. Only Complete Express and Speedy Express packages are available for orders under or equal to 1 day."
            )
            print("\nHere is Your Payment")
            print(f"Package: {self.desc}")
            print(f"Quantity: {self.ko} Kilogram")
            print(f"Processing time: {self.dy} Day")
            print(f"Total Payment: Rp{tpy}")
            print("\nThank You for Ordering")
            return (
                tpy  # You can change this to a blank string when you not doing unit testing
            )
   
    # Test the calculation
    order = calcPayment(4, 4, 1)  # calcPayment(package, quantity, processing time(day))
    print(order.countTotal())
   

3. Writing Unit Testing

   To ensure our calcPayment class works correctly, we need to write unit tests using the unittest library. Here's how to do it:

   Create file with name test_hitung_harga.py

    import unittest
    import sys
   
    # Adjust path according the file location
    sys.path.append(
        "Your\Path" # Example "C:\Coding\Unit Testing"
    )
   
    from laundryCode.hitungHarga import calcPayment
   
    class TestCalculations(unittest.TestCase):
   
        def setUp(self):
            self.tp1 = calcPayment(1, 2, 5)
            self.tp2 = calcPayment(2, 5, 3)
            self.tp3 = calcPayment(3, 5, 1)
            self.tp4 = calcPayment(4, 4, 1)
   
        def test_calculation_FDC(self):
            self.assertEqual(self.tp1.countTotal(), 21000.0, "Incorrect calculation")
   
        def test_calculation_IDC(self):
            self.assertEqual(self.tp2.countTotal(), 50000.0, "Incorrect calculation")
   
        def test_calculation_CEP(self):
            self.assertEqual(self.tp3.countTotal(), 75000.0, "Incorrect calculation")
   
        def test_calculation_SEP(self):
            self.assertEqual(self.tp4.countTotal(), 100000.0, "Incorrect calculation")
   
    if __name__ == "__main__":
        unittest.main(buffer=True)  # Ignore text from class
   

   This test suite covers various scenarios for each package type, ensuring that the calcPayment class handles different inputs correctly.

4. Run the Program

   Run the program with your terminal or IDE.

   

   Well, LGTM!

5. Source Code

   You can see the source code here.

Conclusion

Unit testing is an essential practice in software development. It helps ensure the accuracy and reliability of your code by identifying bugs early in the development process. By implementing unit tests for our calcPayment class, we can confidently calculate laundry prices and handle various input scenarios without errors.

I hope this guide has provided you with a clear understanding of how to write and run unit tests in Python. Happy coding!

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👋 Hello, I’m Abdiel, 1st Year Informatics Student, Programmer, and Freelancer.

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