pythonpytest

VIN Discrepancies

Ben Gorman

Ben Gorman

Life's a garden. Dig it.

You run a car dealership :material-car-side:. The inventory is tracked in two places: a database and a text file, each of which contain a set of Vehicle Identification Numbers (VINs).

They should have the same set of VINs (not necessarily in the same order).

Write a test that checks for discrepancies in the VINs. If differences exist, provide a useful message to the user for fixing them.

Directory Structure

vins/
  vins.txt
  vins.py
  test_vins.py

Files

WP0AA2991YS620631
1G4GJ11Y9HP422546
4T1BG22K8VU176482
JH4KA3151KC019450
1FTYR14U2XPC03940
JH4DC4340RS000837
JH4DA9340MS002938
JH4DB1660LS017594
1GCDC14K2LE198114
JH4NA1260MT001906
2FMDA5146TBC22506
def fetch_vins_from_db():
    """Pretend to fetch VINs from a database.."""
 
    vins = [
        "WP0AA2991YS620631",
        "JH4NA1150RT000268",
        "4T1BG22K8VU176482",
        "JH4KA3151KC019450",
        "1FTYR14U2XPC03940",
        "5GAEV23718J129013",
        "JH4DA9340MS002938",
        "JH4DB1660LS017594",
        "1GCDC14K2LE198114",
        "JH4NA1260MT001906",
        "JH4DA3441JS029234",
        "5TFUW5F13CX228552",
    ]
 
    return vins
from vins import fetch_vins_from_db
 
def test_vin_discrepancies():
    """Check for discrepancies in VINs between vins.txt and the database"""
    
    # your code here

Solution

test_vins.py
from vins import fetch_vins_from_db
 
def test_vin_discrepancies():
    """Check for discrepancies in VINs between vins.txt and the database"""
 
    # load VINs from database
    vins_db = fetch_vins_from_db()
 
    # Load VINs from text file
    vins_file = open('vins.txt', 'r')
    vins_txt = vins_file.read().splitlines()
 
    # Convert to sets for easy comparison
    vins_db = set(vins_db)
    vins_txt = set(vins_txt)
 
    # Check for VINs in db not in txt and vice versa
    vins_db_not_tx = vins_db - vins_txt
    vins_txt_not_db = vins_txt - vins_db
 
    assert len(vins_db_not_tx) == 0 and len(vins_txt_not_db) == 0, \
        f"VIN discrepancies found!\n" \
        f"VINs in database not in vins.txt: {vins_db_not_tx}\n" \
        f"VINs in vins.txt not in database: {vins_txt_not_db}"

Explanation

The strategy here is to represent each collection of VINs as a set. Then we can use set differences to get the values in one set not in the other.

In order to report a useful error message, we place an f-string alongside the assertion as described here.