🧪 testing-containers

Lightweight Python utilities for running ephemeral Docker containers in tests. Includes TestingPostgres for disposable PostgreSQL test databases and DockerContainer for ad-hoc containers.

🚀 Overview

testing-containers helps you run real services inside Docker for integration or functional tests — without ever needing to manually start external databases, message brokers or anything else.

It provides:

• TestingPostgres — a PostgreSQL-specific helper that automatically creates a fresh empty test database before tests start and tears it down afterwards.
• DockerContainer — a generic helper to start, stop, and execute commands inside any Docker container (Postgres, Redis, LocalStack, etc.).

The goal is simple:

Make your tests fully isolated, reproducible, and environment-agnostic — no shared state, no external dependencies.

🧭 Design Principles

• 🧩 No external services need to be manually started
• 🔁 Fresh empty databases are created every test run
• 🧹 Automatic cleanup when tests finish
• 🧱 No pollution of your dev DB — tests never touch your development data
• ⚙️ Consistent environments — use the same database version as production via Docker
• 🧰 Generic & extensible — same approach works for PostgreSQL, Redis, LocalStack, RabbitMQ, etc.
• 🐳 Only dependency: Docker (required only when containers are used)

⚙️ Installation

pip install testing-containers

Requires Docker installed and running if you plan to spin up containerized services.

💡 Usage

TestingPostgres

You can use TestingPostgres in two ways

a) Run Postgres inside Docker

import psycopg
from testing_containers import TestingPostgres, ContainerOptions

pg = TestingPostgres(
    options=ContainerOptions(
        namespace="myproject-name" # optional – you can add a namespace to the container
        name="testdb" # optional – you can give a name to the container
        image="postgres:15.6" # optional / default postgres:16.3
        # The following options defines what should happen on stop()
        # container will stop or not
        # container will be removed or not
        # (you can decide on the speed you want on test startup and teardown)
        should_stop=True # optional / default=False
        remove_on_stop=True # optional / default=False
    )
)  # spins up a postgres:16.3 container
testdb = pg.postgres.testdb  # connection info for your test DB

# Connect and run migrations or tests
conn = psycopg.connect(
    dbname=testdb.name,
    user=testdb.user,
    password=testdb.password,
    host=testdb.host,
    port=testdb.port,
)
print("Connected:", conn)

# After tests
pg.stop()

b) Connect to an existing Postgres instance

❗ Important: In case the provided database is not available/ready it will spin a postgres container and use that as a fallback

from testing_containers import TestingPostgres, DBConfig

dev_db_config = DBConfig(
    host="localhost",
    name="dev_db",
    user="postgres",
    password="secret",
    port=5432,
)
pg = TestingPostgres(db_config=dev_db_config)
print(pg.testdb)  # e.g. "test_dev_db" — a fresh copy created on the fly
# ... run tests ...
pg.stop()  # drops the test DB

✅ Each run creates a temporary database (test_<original_dbname>) and destroys it afterwards.

Example: using pytests, alembic and settings on conftest

• You run TestingPostgres
• You mock DB environment variables to the one of TestingPostgres().postgres.test_db
• So your app during tests runtime will be connected to testdb
• Create a pytest fixture which run alembic migration on start and stops testdb(drops testdb) on teardown

import os
import pytest
from unittest.mock import patch
from alembic import command
from alembic.config import Config
from testing_containers import TestingPostgres

testing = TestingPostgres()
testdb = testing.postgres.test_db

env_vars = {
    "DB__USER": testdb.db.user,
    "DB__PASSWORD": testdb.db.password,
    "DB__HOST": testdb.db.host,
    "DB__PORT": str(testdb.db.port),
    "DB__NAME": testdb.db.name,
}
with patch.dict(os.environ, env_vars):
    from app.settings import settings


@pytest.fixture(scope="session", autouse=True)
def setup_test_db():
    """Setup and teardown for the test db"""
    # Run Alembic migrations
    # Ensure the path to alembic.ini is correct
    alembic_cfg = Config("alembic.ini")
    try:
        command.upgrade(alembic_cfg, "head")
    except Exception:
        raise

    yield

    testdb.stop() # Tear down test db

Generic DockerContainer

Start any service container on demand — e.g. Redis:

from testing_containers import DockerContainer

redis = DockerContainer(
    container_name="test-redis",
    image="redis:7",
    expose_ports=["6379:6379"]
)

redis.start_container()
result = redis.exec(["redis-cli", "ping"])
print(result.stdout.strip())  # → PONG
redis.stop_container()
redis.remove_container()

✅ Great for spinning up ad-hoc containers for any dependency during tests.

🧠 Why use this

🧪 Requirements

• Python 3.10+
• Docker (required only for containerized tests)

💡 Inspiration

This project was inspired by testing.postgresql package, which provides temporary PostgreSQL instances for testing.

However, testing.postgresql requires PostgreSQL to be installed locally on the developer’s machine. That can lead to common issues in real-world teams:

• Developers might have different PostgreSQL versions installed.
• Local PostgreSQL configuration may differ from the production environment.
• Installing or managing Postgres locally can be slow or error-prone in CI and requires additional setup

testing-containers solves these problems by leveraging Docker:

• No local Postgres installation required.
• The same Postgres (or Redis, MariaDB, etc.) version used in production can be pulled and run in tests.
• Works identically on any environment — macOS, Linux, Windows, or CI/CD runners.

In short, it keeps the convenience of testing.postgresql while ensuring environment parity and zero setup.

🧾 License

MIT © Tedi Cela