Dexter

Python Automation Best Practices

This guide collects automation engineering best practices applied throughout Dexter. Use it as a reference when writing or reviewing test code.

Project Structure

Keep tests and source code clearly separated:

tests/
├── api/          ← API test modules
├── ui/           ← UI (Selenium) test modules
└── conftest.py   ← Shared fixtures and configuration

Data-Driven Tests

Use pytest.mark.parametrize to test multiple inputs without duplicating code:

import pytest

@pytest.mark.parametrize("item,price,qty,expected_status", [
    ("Widget", 9.99, 2, 201),
    ("",       9.99, 2, 400),   # missing item
    ("Widget", -1,   2, 400),   # negative price
])
def test_create_order_validation(client, item, price, qty, expected_status):
    response = client.post("/api/orders", json={"item": item, "price": price, "qty": qty})
    assert response.status_code == expected_status

Explicit Waits in Selenium

Never use time.sleep. Use WebDriverWait with expected conditions:

from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC
from selenium.webdriver.common.by import By

wait = WebDriverWait(driver, timeout=10)

# Wait until an element is visible
element = wait.until(EC.visibility_of_element_located((By.ID, "order-list")))

# Wait until text appears
wait.until(EC.text_to_be_present_in_element((By.ID, "status"), "Success"))

Set a sensible default timeout (10 seconds) and document why a longer timeout is needed if you use one.

Logging

Use Python’s built-in logging module instead of print statements in application code:

import logging

logger = logging.getLogger(__name__)

def create_order(order_data):
    logger.info("Creating order: %s", order_data)
    # ...

In tests, print is acceptable for quick debugging but should be removed before merging.

Error Handling

# Good
try:
    result = process_order(data)
except ValueError as exc:
    logger.error("Invalid order data: %s", exc)
    return {"error": str(exc)}, 400

# Avoid
try:
    result = process_order(data)
except:
    return {"error": "Something went wrong"}, 500

Naming Conventions

Item Convention Example
Test file test_<feature>.py test_orders_api.py
Test function test_<behaviour>_<condition> test_delete_order_returns_204
Fixture descriptive noun client, browser, sample_order
Variable snake_case order_id, response_body
Constant UPPER_SNAKE_CASE BASE_URL, DEFAULT_TIMEOUT

Code Review Checklist

Before submitting a PR, verify each item:

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