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Write tests with Testcontainers

Table of contents

You'll create a PostgreSQL container using Testcontainers and use it for all the tests. Before each test, you'll delete all customer records so that tests run with a clean database.

Set up pytest fixtures

This guide uses pytest fixtures for setup and teardown logic. A recommended approach is to use finalizers to guarantee cleanup runs even if setup fails:

@pytest.fixture
def setup(request):
    # setup code

    def cleanup():
        # teardown code

    request.addfinalizer(cleanup)
    return some_value

Create the test file

Create a tests/__init__.py file with empty content to enable pytest auto-discovery.

Then create tests/test_customers.py with the fixtures:

import os
import pytest
from testcontainers.postgres import PostgresContainer

from customers import customers

postgres = PostgresContainer("postgres:16-alpine")


@pytest.fixture(scope="module", autouse=True)
def setup(request):
    postgres.start()

    def remove_container():
        postgres.stop()

    request.addfinalizer(remove_container)
    os.environ["DB_CONN"] = postgres.get_connection_url()
    os.environ["DB_HOST"] = postgres.get_container_host_ip()
    os.environ["DB_PORT"] = str(postgres.get_exposed_port(5432))
    os.environ["DB_USERNAME"] = postgres.username
    os.environ["DB_PASSWORD"] = postgres.password
    os.environ["DB_NAME"] = postgres.dbname
    customers.create_table()


@pytest.fixture(scope="function", autouse=True)
def setup_data():
    customers.delete_all_customers()

Here's what the fixtures do:

  • The setup fixture has scope="module", so it runs once for all tests in the file. It starts a PostgreSQL container, sets environment variables with the connection details, and creates the customers table. A cleanup function removes the container after all tests complete.
  • The setup_data fixture has scope="function", so it runs before every test. It deletes all records to give each test a clean database.

Write the tests

Add the test functions to the same file:

def test_get_all_customers():
    customers.create_customer("Siva", "siva@gmail.com")
    customers.create_customer("James", "james@gmail.com")
    customers_list = customers.get_all_customers()
    assert len(customers_list) == 2


def test_get_customer_by_email():
    customers.create_customer("John", "john@gmail.com")
    customer = customers.get_customer_by_email("john@gmail.com")
    assert customer.name == "John"
    assert customer.email == "john@gmail.com"
  • test_get_all_customers() inserts two customer records, fetches all customers, and asserts the count.
  • test_get_customer_by_email() inserts a customer, fetches it by email, and asserts the details.

Because setup_data deletes all records before each test, the tests can run in any order.

Run tests and next steps »