refactor: split database model tests into organized modules

Split the monolithic test_database_models.py into focused test modules:

Database model tests (tests/unit/models/database/):
- test_customer.py: Customer model and authentication tests
- test_inventory.py: Inventory model tests
- test_marketplace_import_job.py: Import job model tests
- test_marketplace_product.py: Marketplace product model tests
- test_order.py: Order and OrderItem model tests
- test_product.py: Product model tests
- test_team.py: Team invitation and membership tests
- test_user.py: User model tests
- test_vendor.py: Vendor model tests

Schema validation tests (tests/unit/models/schema/):
- test_auth.py: Auth schema validation tests
- test_customer.py: Customer schema validation tests
- test_inventory.py: Inventory schema validation tests
- test_marketplace_import_job.py: Import job schema tests
- test_order.py: Order schema validation tests
- test_product.py: Product schema validation tests

This improves test organization and makes it easier to find
and maintain tests for specific models.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/unit/models/database/test_inventory.py

@@ -0,0 +1,143 @@
+# tests/unit/models/database/test_inventory.py
+"""Unit tests for Inventory database model."""
+import pytest
+from sqlalchemy.exc import IntegrityError
+
+from models.database.inventory import Inventory
+
+
+@pytest.mark.unit
+@pytest.mark.database
+class TestInventoryModel:
+    """Test Inventory model."""
+
+    def test_inventory_creation_with_product(self, db, test_vendor, test_product):
+        """Test Inventory model linked to product."""
+        inventory = Inventory(
+            product_id=test_product.id,
+            vendor_id=test_vendor.id,
+            location="WAREHOUSE_A",
+            quantity=150,
+            reserved_quantity=10,
+            gtin=test_product.marketplace_product.gtin,
+        )
+
+        db.add(inventory)
+        db.commit()
+        db.refresh(inventory)
+
+        assert inventory.id is not None
+        assert inventory.product_id == test_product.id
+        assert inventory.vendor_id == test_vendor.id
+        assert inventory.location == "WAREHOUSE_A"
+        assert inventory.quantity == 150
+        assert inventory.reserved_quantity == 10
+        assert inventory.available_quantity == 140  # 150 - 10
+
+    def test_inventory_unique_product_location(self, db, test_vendor, test_product):
+        """Test unique constraint on product_id + location."""
+        inventory1 = Inventory(
+            product_id=test_product.id,
+            vendor_id=test_vendor.id,
+            location="WAREHOUSE_A",
+            quantity=100,
+        )
+        db.add(inventory1)
+        db.commit()
+
+        # Same product + location should fail
+        with pytest.raises(IntegrityError):
+            inventory2 = Inventory(
+                product_id=test_product.id,
+                vendor_id=test_vendor.id,
+                location="WAREHOUSE_A",
+                quantity=50,
+            )
+            db.add(inventory2)
+            db.commit()
+
+    def test_inventory_same_product_different_location(self, db, test_vendor, test_product):
+        """Test same product can have inventory in different locations."""
+        inventory1 = Inventory(
+            product_id=test_product.id,
+            vendor_id=test_vendor.id,
+            location="WAREHOUSE_A",
+            quantity=100,
+        )
+        db.add(inventory1)
+        db.commit()
+
+        # Same product in different location should succeed
+        inventory2 = Inventory(
+            product_id=test_product.id,
+            vendor_id=test_vendor.id,
+            location="WAREHOUSE_B",
+            quantity=50,
+        )
+        db.add(inventory2)
+        db.commit()
+        db.refresh(inventory2)
+
+        assert inventory2.id is not None
+        assert inventory2.location == "WAREHOUSE_B"
+
+    def test_inventory_default_values(self, db, test_vendor, test_product):
+        """Test Inventory model default values."""
+        inventory = Inventory(
+            product_id=test_product.id,
+            vendor_id=test_vendor.id,
+            location="DEFAULT_LOC",
+            quantity=100,
+        )
+        db.add(inventory)
+        db.commit()
+        db.refresh(inventory)
+
+        assert inventory.reserved_quantity == 0  # Default
+        assert inventory.available_quantity == 100  # quantity - reserved
+
+    def test_inventory_available_quantity_property(self, db, test_vendor, test_product):
+        """Test available_quantity computed property."""
+        inventory = Inventory(
+            product_id=test_product.id,
+            vendor_id=test_vendor.id,
+            location="PROP_TEST",
+            quantity=200,
+            reserved_quantity=50,
+        )
+        db.add(inventory)
+        db.commit()
+        db.refresh(inventory)
+
+        assert inventory.available_quantity == 150  # 200 - 50
+
+    def test_inventory_relationships(self, db, test_vendor, test_product):
+        """Test Inventory relationships."""
+        inventory = Inventory(
+            product_id=test_product.id,
+            vendor_id=test_vendor.id,
+            location="REL_TEST",
+            quantity=100,
+        )
+        db.add(inventory)
+        db.commit()
+        db.refresh(inventory)
+
+        assert inventory.product is not None
+        assert inventory.vendor is not None
+        assert inventory.product.id == test_product.id
+        assert inventory.vendor.id == test_vendor.id
+
+    def test_inventory_without_gtin(self, db, test_vendor, test_product):
+        """Test Inventory can be created without GTIN."""
+        inventory = Inventory(
+            product_id=test_product.id,
+            vendor_id=test_vendor.id,
+            location="NO_GTIN",
+            quantity=100,
+        )
+        db.add(inventory)
+        db.commit()
+        db.refresh(inventory)
+
+        assert inventory.gtin is None