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Testing and CI/CD

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flask is a python full-stack framework.
flask is a python full-stack framework.
By Mulugega Mehari
6 min read
Testing and CI/CD

Lesson Plan: Testing and CI/CD in Python with pytest, GitHub Actions, and Docker

Objective:

By the end of this lesson, students will be able to:

  1. Write unit tests in Python using pytest.
  2. Set up Continuous Integration (CI) using GitHub Actions.
  3. Containerize a Python application using Docker.
  4. Implement Continuous Deployment (CD) using Docker and GitHub Actions.

Lesson Outline

1. Introduction (15 minutes)

  • What is Testing?
    • Importance of testing in software development.
    • Types of tests: unit, integration, end-to-end.
  • What is CI/CD?
    • Continuous Integration (CI): Automatically testing code changes.
    • Continuous Deployment (CD): Automatically deploying code changes.
  • Tools Overview:
    • pytest: A testing framework for Python.
    • GitHub Actions: A CI/CD tool integrated with GitHub.
    • Docker: A tool to containerize applications.

2. Writing Tests with pytest (30 minutes)

  • Installation:
    1

    pip install pytest
  • Writing a Simple Test:
    • Create a Python file calculator.py:
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      def add(a, b):
    return a + b

def subtract(a, b):
    return a - b
    • Create a test file test_calculator.py:
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      from calculator import add, subtract

def test_add():
    assert add(2, 3) == 5
    assert add(-1, 1) == 0

def test_subtract():
    assert subtract(5, 3) == 2
    assert subtract(10, 7) == 3
  • Running Tests:
    1

    pytest
  • Explanation:
    • assert: Checks if the condition is true; if not, the test fails.
    • pytest automatically discovers and runs tests in files named test_*.py.

3. Setting Up CI with GitHub Actions (30 minutes)

  • What is GitHub Actions?
    • A CI/CD tool that allows you to automate workflows.
  • Creating a Workflow:
    • Create a .github/workflows/ci.yml file:
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      name: CI

on:
  push:
    branches:
      - main
  pull_request:
    branches:
      - main

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - name: Set up Python
        uses: actions/setup-python@v2
        with:
          python-version: '3.9'
      - name: Install dependencies
        run: |
          python -m pip install --upgrade pip
          pip install pytest
      - name: Run tests
        run: pytest
  • Explanation:
    • on: Specifies when the workflow should run (e.g., on push or pull request).
    • jobs: Defines the jobs to run (e.g., test).
    • steps: The steps to execute in the job (e.g., install Python, run tests).

4. Containerizing the Application with Docker (30 minutes)

  • What is Docker?
    • A tool to package applications into containers.
  • Creating a Dockerfile:
    • Create a Dockerfile:
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      # Use an official Python runtime as a parent image
FROM python:3.9-slim

# Set the working directory in the container
WORKDIR /app

# Copy the current directory contents into the container
COPY . .

# Install any needed packages specified in requirements.txt
RUN pip install --no-cache-dir -r requirements.txt

# Run tests
RUN pytest

# Make port 80 available to the world outside this container
EXPOSE 80

# Run the application
CMD ["python", "app.py"]
  • Building and Running the Docker Image:
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    docker build -t my-python-app .
docker run -p 4000:80 my-python-app
  • Explanation:
    • FROM: Specifies the base image.
    • WORKDIR: Sets the working directory.
    • COPY: Copies files from the host to the container.
    • RUN: Executes commands (e.g., install dependencies, run tests).
    • EXPOSE: Exposes a port.
    • CMD: Specifies the command to run the application.

5. Implementing CD with GitHub Actions and Docker (30 minutes)

  • Extending the Workflow:
    • Update .github/workflows/ci.yml to include CD:
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      name: CI/CD

on:
  push:
    branches:
      - main
  pull_request:
    branches:
      - main

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - name: Set up Python
        uses: actions/setup-python@v2
        with:
          python-version: '3.9'
      - name: Install dependencies
        run: |
          python -m pip install --upgrade pip
          pip install pytest
      - name: Run tests
        run: pytest

  deploy:
    needs: test
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - name: Build Docker image
        run: docker build -t my-python-app .
      - name: Log in to Docker Hub
        run: echo "$" | docker login -u "$" --password-stdin
      - name: Push Docker image
        run: docker push my-python-app
  • Explanation:
    • deploy: A new job that builds and pushes the Docker image.
    • needs: test: Ensures the deploy job runs only if the test job succeeds.
    • secrets.DOCKER_USERNAME and secrets.DOCKER_PASSWORD: GitHub secrets for Docker Hub credentials.

6. Recap and Q&A (15 minutes)

  • Recap the key concepts: testing, CI/CD, Docker.
  • Answer any questions from students.

Flashcards for Retention

  1. Q: What is pytest used for?
    A: A testing framework for Python to write and run tests.

  2. Q: How do you run tests using pytest?
    A: Run pytest in the terminal.

  3. Q: What is Continuous Integration (CI)?
    A: Automatically testing code changes.

  4. Q: What is Continuous Deployment (CD)?
    A: Automatically deploying code changes.

  5. Q: What is GitHub Actions?
    A: A CI/CD tool integrated with GitHub.

  6. Q: What is Docker?
    A: A tool to containerize applications.

  7. Q: What does the FROM command in a Dockerfile do?
    A: Specifies the base image.

  8. Q: What does the WORKDIR command in a Dockerfile do?
    A: Sets the working directory in the container.

  9. Q: What does the COPY command in a Dockerfile do?
    A: Copies files from the host to the container.

  10. Q: What does the RUN command in a Dockerfile do?
    A: Executes commands (e.g., install dependencies, run tests).

  11. Q: What does the EXPOSE command in a Dockerfile do?
    A: Exposes a port to the outside world.

  12. Q: What does the CMD command in a Dockerfile do?
    A: Specifies the command to run the application.

  13. Q: How do you build a Docker image?
    A: Run docker build -t <image-name> .

  14. Q: How do you run a Docker container?
    A: Run docker run -p <host-port>:<container-port> <image-name>

  15. Q: What is the purpose of the on key in a GitHub Actions workflow?
    A: Specifies when the workflow should run (e.g., on push or pull request).

  16. Q: What is the purpose of the jobs key in a GitHub Actions workflow?
    A: Defines the jobs to run (e.g., test, deploy).

  17. Q: What is the purpose of the steps key in a GitHub Actions workflow?
    A: The steps to execute in the job (e.g., install Python, run tests).

  18. Q: How do you log in to Docker Hub in a GitHub Actions workflow?
    A: Use echo "$" | docker login -u "$" --password-stdin

  19. Q: How do you push a Docker image to Docker Hub in a GitHub Actions workflow?
    A: Use docker push <image-name>

  20. Q: What is the purpose of the needs key in a GitHub Actions workflow?
    A: Ensures a job runs only if another job succeeds.

Conclusion

This lesson plan provides a comprehensive guide to testing and CI/CD in Python using pytest, GitHub Actions, and Docker. The practical examples, code block comments, and flashcards will help reinforce the concepts and ensure retention.

Additional resources

  • Github Actions for Continuous Integration (CI) by Wes Doyle

  • CS50W - Lecture 7 - Testing and CI/CD

  • Slides for CS50W(for the above video)

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