1 - app\__init__.py

from flask import Flask

def create_app():
    app = Flask('testapp')
    
    # omitted for brevity: load app config

    # configure database
    from app.lib.db import init_engine, db_session
    init_engine(app.config['DATABASE_URI'])

    # close database session during teardown
    @app.teardown_appcontext
    def shutdown_session(exception=None):
        db_session.remove()

    from app.example import bp
    app.register_blueprint(bp)

    return app

if __name__ == "__main__":
    app = create_app()
    app.run()

2 - app\db.py

from sqlalchemy import create_engine
from sqlalchemy.orm import scoped_session, sessionmaker
from sqlalchemy.ext.declarative import declarative_base

engine = None
made_session = sessionmaker(autocommit=False)
db_session = scoped_session(made_session)
Base = declarative_base()

def init_engine(uri):
    global made_session, engine, session, Base

    engine = create_engine(uri, echo=True, pool_pre_ping=True)
    db_session.remove()
    made_session.configure(bind=engine)
    Base.query = db_session.query_property()

def init_db():
    Base.metadata.create_all(bind=engine)

3 - app\example.py

from flask import Blueprint
from app.models.person import Person
from app.db import db_session

bp = Blueprint('example', __name__, url_prefix='/example')

@bp.route('/form', methods = ['POST'])
def test_form():
    return str(db_session.query(Person).count())

@bp.route('/json', methods = ['POST'])
def test_json():
    return str(db_session.query(Person).count())

4 - app\models\person.py

from sqlalchemy import Column, String
from app.lib.db import Base, db_session

class Person(Base):
    __tablename__ = 'people'

    id = Column(String, primary_key=True)

5 - tests\conftest.py

import pytest
from app import create_app

@pytest.fixture(scope='session')
def client():
    """A test instance of the app in testing mode"""
    app = create_app()
    client = app.test_client()
    yield client

6 - tests\people\person_factories.py

import factory
from app.lib.db import db_session
from app.models.person import Person

class PersonFactory(factory.alchemy.SQLAlchemyModelFactory):
    class Meta:
        model = Person
        sqlalchemy_session = db_session

    id = factory.Faker('uuid4')

7 - tests\test_example.py

from flask import json
from tests.people.person_factories import PersonFactory

class TestExample:
    def test_form(self, client):
        person = PersonFactory()
        resp = client.post('/example/form', data={'foo': 'bar'})
        assert resp.data == b'1'

    def test_json(self, client):
        person = PersonFactory()
        resp = client.post('/example/json', json={'foo': 'bar'})
        assert resp.data == b'1'