Re-factor the ORM tests to use randomized fake data

- create `*Factory` classes with fakerboy and faker that generate
  randomized instances of the ORM models
- add new pytest marker: "db" are the integration tests involving the
  database whereas "e2e" will be all other integration tests
- streamline the docstrings in the ORM models

tests/db/fake_data/fixture_makers.py

@@ -0,0 +1,105 @@
+"""Fixture factories for testing the ORM layer with fake data."""
+
+import pytest
+
+from tests.db.fake_data import factories
+
+
+@pytest.fixture
+def make_address(city):
+    """Replaces `AddressFactory.build()`: Create an `Address` in the `city`."""
+    # Reset the identifiers before every test.
+    factories.AddressFactory.reset_sequence(1)
+
+    def func(**kwargs):
+        """Create an `Address` object in the `city`."""
+        return factories.AddressFactory.build(city=city, **kwargs)
+
+    return func
+
+
+@pytest.fixture
+def make_courier():
+    """Replaces `CourierFactory.build()`: Create a `Courier`."""
+    # Reset the identifiers before every test.
+    factories.CourierFactory.reset_sequence(1)
+
+    def func(**kwargs):
+        """Create a new `Courier` object."""
+        return factories.CourierFactory.build(**kwargs)
+
+    return func
+
+
+@pytest.fixture
+def make_customer():
+    """Replaces `CustomerFactory.build()`: Create a `Customer`."""
+    # Reset the identifiers before every test.
+    factories.CustomerFactory.reset_sequence(1)
+
+    def func(**kwargs):
+        """Create a new `Customer` object."""
+        return factories.CustomerFactory.build(**kwargs)
+
+    return func
+
+
+@pytest.fixture
+def make_restaurant(make_address):
+    """Replaces `RestaurantFactory.build()`: Create a `Restaurant`."""
+    # Reset the identifiers before every test.
+    factories.RestaurantFactory.reset_sequence(1)
+
+    def func(address=None, **kwargs):
+        """Create a new `Restaurant` object.
+
+        If no `address` is provided, a new `Address` is created.
+        """
+        if address is None:
+            address = make_address()
+
+        return factories.RestaurantFactory.build(address=address, **kwargs)
+
+    return func
+
+
+@pytest.fixture
+def make_order(make_address, make_courier, make_customer, make_restaurant):
+    """Replaces `OrderFactory.build()`: Create a `Order`."""
+    # Reset the identifiers before every test.
+    factories.AdHocOrderFactory.reset_sequence(1)
+
+    def func(scheduled=False, restaurant=None, courier=None, **kwargs):
+        """Create a new `Order` object.
+
+        Each `Order` is made by a new `Customer` with a unique `Address` for delivery.
+
+        Args:
+            scheduled: if an `Order` is a pre-order
+            restaurant: who receives the `Order`; defaults to a new `Restaurant`
+            courier: who delivered the `Order`; defaults to a new `Courier`
+            kwargs: additional keyword arguments forwarded to the `OrderFactory`
+
+        Returns:
+            order
+        """
+        if scheduled:
+            factory_cls = factories.ScheduledOrderFactory
+        else:
+            factory_cls = factories.AdHocOrderFactory
+
+        if restaurant is None:
+            restaurant = make_restaurant()
+        if courier is None:
+            courier = make_courier()
+
+        return factory_cls.build(
+            customer=make_customer(),  # assume a unique `Customer` per order
+            restaurant=restaurant,
+            courier=courier,
+            pickup_address=restaurant.address,  # no `Address` history
+            delivery_address=make_address(),  # unique `Customer` => new `Address`
+            **kwargs,
+        )
+
+    return func