Does Flask Work With Cypress?
Flask and Cypress work together seamlessly for end-to-end testing of Python web applications.
Quick Facts
How Flask Works With Cypress
Flask serves as your backend application while Cypress runs in a separate Node.js process to test it via the browser. This is a natural pairing since Cypress is framework-agnostic and simply makes HTTP requests to your running Flask server. You start your Flask development server on a local port (typically 5000), configure Cypress to point to that base URL, and write tests that interact with your application through the browser. The developer experience is excellent: Flask's hot-reload pairs well with Cypress's interactive test runner, allowing you to iterate quickly. Cypress can inspect network requests, manipulate local storage, and even stub API responses if your Flask app serves an SPA frontend. No special plugins or adapters are needed—just standard HTTP communication. The only architectural consideration is ensuring your Flask app runs during test execution, which is trivial in development but requires a test fixture or start script in CI/CD pipelines.
Best Use Cases
Flask + Cypress Integration Setup
npm install --save-dev cypress && pip install flask// cypress/e2e/auth.cy.js
describe('Flask Authentication Flow', () => {
beforeEach(() => {
cy.visit('http://localhost:5000')
})
it('should login and access protected page', () => {
cy.get('input[name="username"]').type('testuser')
cy.get('input[name="password"]').type('password123')
cy.get('button[type="submit"]').click()
cy.url().should('include', '/dashboard')
cy.get('h1').should('contain', 'Welcome')
})
it('should display error on invalid credentials', () => {
cy.get('input[name="username"]').type('testuser')
cy.get('input[name="password"]').type('wrongpass')
cy.get('button[type="submit"]').click()
cy.get('.alert').should('contain', 'Invalid credentials')
})
})
// app.py (Flask)
from flask import Flask, render_template, request, redirect
app = Flask(__name__)
@app.route('/')
def index():
return render_template('login.html')
@app.route('/login', methods=['POST'])
def login():
if request.form.get('password') == 'password123':
return redirect('/dashboard')
return render_template('login.html', error='Invalid credentials')
@app.route('/dashboard')
def dashboard():
return '<h1>Welcome</h1>'Known Issues & Gotchas
Flask development server isn't accessible from tests due to CORS or localhost binding
Fix: Ensure Flask binds to 0.0.0.0 or configure Cypress baseUrl correctly. In tests, use cy.visit('http://localhost:5000/path') and set FLASK_ENV=development
Test database state persists between test runs, causing flaky tests
Fix: Use Flask fixtures or a conftest.py to reset the database before each test. Create a dedicated test database and tear it down after test suites complete
Cypress struggles with Flask session-based authentication if not properly configured
Fix: Use cy.session() to manage login state across tests, or create helper commands that POST to your Flask login endpoint and preserve cookies
CSRF token validation blocks POST requests in tests
Fix: Extract CSRF tokens from the page using cy.get() and include them in request headers, or disable CSRF protection in test configuration
Alternatives
- •Django + Cypress: Django's ORM and test utilities pair well with Cypress for full Python web stacks
- •FastAPI + Cypress: Modern async Python framework with excellent OpenAPI docs, pairs naturally with Cypress for API testing
- •Flask + Selenium: Traditional Python-based E2E testing, but slower and less developer-friendly than Cypress
Resources
Related Compatibility Guides
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