Traffic Fine Calculator — Pytest CSV Demo

This project demonstrates how to write clean, scalable, and maintainable automated tests using pytest-csv-params, a plugin that allows loading test cases from CSV files.

The core example is a function that calculates traffic fines based on speeding severity, zone type, and driver penalty points.

Project Structure

.
├── calculate_traffic_fine_tests.csv      # Test data in CSV format
├── test_csv_params.py                    # Main test file using pytest-csv-params
├── test_params.py                        # Classic pytest.mark.parametrize example
├── test_simple.py                        # One-test-per-function approach
├── uut.py                                # Function under test (calculate_traffic_fine)

Function Under Test

The function calculate_traffic_fine() computes fines based on:

• Degree of speeding
• Type of zone (residential, school, highway, construction)
• Driver's license points

Defined in uut.py.

Testing Approaches

This repo demonstrates three ways to structure test data:

File	Strategy
test_simple.py	One test function per case (not scalable)
test_params.py	@pytest.mark.parametrize with inline data
test_csv_params.py	@csv_params loading from external CSV (recommended)

CSV-Based Testing Example

The file calculate_traffic_fine_tests.csv contains test rows like:

speed,limit,zone,license_points,expected,msg
50,50,residential,0,0,No speeding
51,50,highway,0,50,Minimal speeding
51,50,school,0,100,Near school, 2x multiplier
51,50,highway,1,75,Repeat violation

These values are loaded dynamically into tests using:

from pytest_csv_params.decorator import csv_params

@csv_params(
    data_file="calculate_traffic_fine_tests.csv",
    data_casts={
        "speed": int, "limit": int, "license_points": int, "expected": int,
    },
)
def test_calculate_traffic_fine(speed, limit, zone, license_points, expected, msg):
    from uut import calculate_traffic_fine
    assert calculate_traffic_fine(speed, limit, zone, license_points) == expected, msg

Quick Start

1. Clone the repo:

   git clone https://github.com/your-username/traffic-fine-csv-demo
   cd traffic-fine-csv-demo

2. Install dependencies:

   pip install pytest pytest-csv-params

3. Run tests:

   pytest

Dependencies

• Python 3.7+
• pytest
• pytest-csv-params

License

This project is released under the MIT License.

Credits

Created for educational and demonstration purposes as illustration to the blog posts:

• English: https://first.institute/en/blog/how-to-separate-test-data-from-code-csv-pytest/
• Ukrainian: https://first.institute/blog/vidokremyty-dani-vid-kodu-testuvannya-z-csv-pytest/