testcontainers-python

what is it?

core functionality for spinning up docker containers in test environments

examples

testing fastapi and postgresql with pytest

following this guide

requirements.txt

pytest==7.0.1  
testcontainers==3.6.1
testcontainers==4.7.2

conftest.py

launch the postgres container

conftest.py

import pytest
from fastapi.testclient import TestClient
from sqlalchemy import create_engine
from sqlalchemy.orm.session import Session
from testcontainers.core.waiting_utils import wait_for_logs
from testcontainers.postgres import PostgresContainer
 
from database.database import Base
from main import app
from services.v1_0_0.services import get_db
 
POSTGRES_IMAGE = "postgres:14"
POSTGRES_USER = "postgres"
POSTGRES_PASSWORD = "test_password"
POSTGRES_DATABASE = "test_database"
POSTGRES_CONTAINER_PORT = 5432
 
 
@pytest.fixture(scope="session")
def postgres_container() -> PostgresContainer:
    """
    Setup postgres container
    """
    postgres = PostgresContainer(
        image=POSTGRES_IMAGE,
        username=POSTGRES_USER,
        password=POSTGRES_PASSWORD,
        dbname=POSTGRES_DATABASE,
        port=POSTGRES_CONTAINER_PORT,
    )
    with postgres:
        wait_for_logs(
            postgres,
            r"UTC \[1\] LOG:  database system is ready to accept connections",
            10,
        )
        yield postgres

create the engine that connects to our test database and initialize the db with the project’s tables

conftest.py

@pytest.fixture(scope="session")
def db(postgres_container: PostgresContainer):
 
    url = postgres_container.get_connection_url()
    engine = create_engine(url, echo=False)
    Base.metadata.create_all(engine)
 
    with Session(engine) as session:
        yield session

override the database dependency as explained in the fastapi documentation, using the injected db fixture that contains our test database

conftest.py

@pytest.fixture(scope="session")
def test_client(db):
    app.dependency_overrides[get_db] = lambda: db
 
    with TestClient(app) as c:
        yield c
 
    app.dependency_overrides.clear()

test_<FOO>.py implementation

test_foo.py

# using the fixtures configured above
 
def create_model_factory(db_session, field):
    model_obj = Model(
        model_field=field,
    )
    db_session.add(model_obj)
    db_session.commit()
 
    return model_obj
 
def test_foo_something(test_client, db)
	field = "foo"
	model_obj = create_model_factory(db, field)
 
	headers = {"X-API-Version": "latest"}
    resp = test_client.get("endpoint/whatever", headers=headers)
 
	assert resp.status_code == 200
	assert resp.json()["model_field"] == "foo"