test_models.py

import pytest
from product.models import Category, Product, Retail

@pytest.fixture
def category(db) -> Category:
    return Category.objects.create(name="Books")

@pytest.fixture
def retailer_abc(db):
    return Retail.objects.create(name="ABC")

@pytest.fixture
def product_one(db, category, retailer_abc):
    product = Product.objects.create(name="Book 1", category=category)
    product.retails.add(retailer_abc)
    return product

def test_product_retailer(db, retailer_abc, product_one):
    assert product_one.retails.filter(name=retailer_abc.name).exists()