Added the first tests to the project. Using factory_boy for great success.

src/requirements/test.txt

@@ -0,0 +1,3 @@
+-r dev.txt
+
+factory_boy==2.10.0

src/shop/factories.py

@@ -0,0 +1,51 @@
+import factory
+
+from factory.django import DjangoModelFactory
+
+from django.utils import timezone
+
+from psycopg2.extras import DateTimeTZRange
+
+from utils.factories import UserFactory
+
+
+class ProductCategoryFactory(DjangoModelFactory):
+    class Meta:
+        model = 'shop.ProductCategory'
+
+    name = factory.Faker('word')
+
+
+class ProductFactory(DjangoModelFactory):
+    class Meta:
+        model = 'shop.Product'
+
+    name = factory.Faker('word')
+    slug = factory.Faker('word')
+    category = factory.SubFactory(ProductCategoryFactory)
+    description = factory.Faker('paragraph')
+    price = factory.Faker('pyint')
+    available_in = factory.LazyFunction(
+        lambda:
+            DateTimeTZRange(
+                lower=timezone.now(),
+                upper=timezone.now() + timezone.timedelta(31)
+            )
+    )
+
+
+class OrderFactory(DjangoModelFactory):
+    class Meta:
+        model = 'shop.Order'
+
+    user = factory.SubFactory(UserFactory)
+
+
+class OrderProductRelationFactory(DjangoModelFactory):
+    class Meta:
+        model = 'shop.OrderProductRelation'
+
+    product = factory.SubFactory(ProductFactory)
+    order = factory.SubFactory(OrderFactory)
+    quantity = 1
+    handed_out = False

src/shop/models.py

@@ -351,7 +351,7 @@ class Product(CreatedUpdatedModel, UUIDModel):
         """
         now = timezone.now()
         time_available = now in self.available_in
-        stock_available = (self.stock_amount - self.left_in_stock()) > 0
+        stock_available = self.left_in_stock() > 0
         return time_available and stock_available
 
     def is_old(self):

src/shop/tests.py

@@ -0,0 +1,30 @@
+from django.test import TestCase
+
+from .factories import (
+    ProductFactory,
+    OrderFactory,
+    OrderProductRelationFactory,
+)
+
+
+class ProductAvailabilityTest(TestCase):
+    """ Test logic about availability of products. """
+
+    def test_product_available_by_stock(self):
+        """ If no orders have been made, the product is still available. """
+        product = ProductFactory(stock_amount=10)
+        self.assertEqual(product.left_in_stock(), 10)
+        self.assertTrue(product.is_available)
+
+    def test_product_not_available_by_stock(self):
+        """ If max orders have been made, the product is NOT available. """
+        product = ProductFactory(stock_amount=2)
+
+        for i in range(2):
+            opr = OrderProductRelationFactory(product=product)
+            order = opr.order
+            order.paid = True
+            order.save()
+
+        self.assertEqual(product.left_in_stock(), 0)
+        self.assertFalse(product.is_available())

src/utils/factories.py

@@ -0,0 +1,11 @@
+import factory
+from factory.django import DjangoModelFactory
+
+
+class UserFactory(DjangoModelFactory):
+    class Meta:
+        model = 'auth.User'
+
+    username = factory.Faker('word')
+    email = factory.Faker('ascii_email')
+