Test containers with Docker in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pytest test using Docker container fixture

What is the output of this pytest test when using the Docker container fixture that starts a Redis container and sets a key?

PyTest

import pytest
import redis

@pytest.fixture(scope='module')
def redis_container(docker_ip, docker_services):
    port = docker_services.port_for('redis', 6379)
    client = redis.Redis(host=docker_ip, port=port)
    docker_services.wait_until_responsive(
        timeout=30.0, pause=0.1,
        check=lambda: client.ping())
    return client

def test_redis_set_get(redis_container):
    redis_container.set('testkey', 'value')
    result = redis_container.get('testkey')
    assert result == b'value'
    print(result)

A b'value' printed and test passes

B b'value' printed but test fails due to assertion error

C Test raises a ConnectionError because Redis is not reachable

D Test raises a SyntaxError due to fixture definition

💡 Hint

The fixture waits until Redis is responsive before returning the client.

The fixture starts a Redis container and waits until it responds to ping. The test sets a key and retrieves it, expecting the byte string b'value'. The assertion passes and the value is printed.

❓ assertion

intermediate

Correct assertion for checking HTTP response in Dockerized test

You run a test against a web service inside a Docker container. Which assertion correctly verifies the HTTP status code is 200?

PyTest

response = client.get('http://localhost:8080/api/data')

A assert response.status == 200

B assert response.status_code == 200

C assert response.code == 200

D assert response.status_code is 200

💡 Hint

Check the attribute name for status code in the response object.

The correct attribute for HTTP status code in most Python HTTP clients is 'status_code'. Using 'is' for integer comparison is not recommended.

🔧 Debug

advanced

Debugging Docker container test failure due to port conflict

A pytest test using a Docker container fails with an error indicating the port 5432 is already in use. What is the most likely cause?

A The Docker container image is missing the PostgreSQL service

B The test code has a syntax error in the port mapping

C Another process on the host machine is using port 5432, causing conflict

D The pytest fixture is not starting the container

💡 Hint

Port conflicts happen when two services try to use the same port on the host.

Port 5432 is the default PostgreSQL port. If another process uses it, Docker cannot bind the container port to the host port, causing failure.

❓ framework

advanced

Choosing the best pytest plugin for Docker container management

Which pytest plugin is designed specifically to manage Docker containers lifecycle during tests?

A pytest-docker

B pytest-mock

C pytest-cov

D pytest-xdist

💡 Hint

Look for a plugin name that includes 'docker'.

pytest-docker helps start and stop Docker containers during pytest runs, making integration testing easier.

🧠 Conceptual

expert

Why use test containers in integration testing?

What is the main advantage of using test containers with Docker in integration testing?

A They automatically generate test data for database tests

B They speed up unit tests by mocking dependencies

C They eliminate the need for writing assertions in tests

D They provide isolated, reproducible environments matching production services

💡 Hint

Think about environment consistency and isolation.

Test containers run real service instances in isolated Docker containers, ensuring tests run in environments similar to production, improving reliability.