Cypress (E2E + Component Testing)

Overview

Cypress runs browser automation with first-class network control, time-travel debugging, and a strong local dev workflow. Use it for critical path E2E tests and for component tests when browser-level rendering matters.

Quick Start

Install and open

npm i -D cypress npx cypress open

Minimal spec

// cypress/e2e/health.cy.ts describe("health", () => { it("loads", () => { cy.visit("/"); cy.contains("Hello").should("be.visible"); }); });

Core Patterns

1. Stable selectors

Prefer data-testid (or data-cy ) attributes for selectors. Avoid brittle CSS chains and text-only selectors for critical interactions.

<button data-testid="save-user">Save</button>

cy.get('[data-testid="save-user"]').click();

2. Deterministic waiting (avoid fixed sleeps)

Wait on app-visible conditions or network aliases rather than cy.wait(1000) .

cy.intercept("GET", "/api/users/*").as("getUser"); cy.visit("/users/1"); cy.wait("@getUser"); cy.get('[data-testid="user-email"]').should("not.be.empty");

3. Network control with cy.intercept

Stub responses for deterministic tests and speed. Keep a small set of “real backend” smoke tests separate.

cy.intercept("GET", "/api/users/1", { statusCode: 200, body: { id: "1", email: "a@example.com" }, }).as("getUser");

4. Authentication strategies

Prefer cy.session to cache login for speed and stability.

// cypress/support/commands.ts Cypress.Commands.add("login", () => { cy.session("user", () => { cy.request("POST", "/api/auth/login", { email: "test@example.com", password: "password", }); }); });

// e2e spec beforeEach(() => { cy.login(); });

Component Testing

Run component tests to validate UI behavior in isolation while keeping browser rendering.

npx cypress open --component

// cypress/component/Button.cy.tsx import React from "react"; import Button from "../../src/Button";

describe("<Button />", () => { it("clicks", () => { cy.mount(<Button onClick={cy.stub().as("onClick")}>Save</Button>); cy.contains("Save").click(); cy.get("@onClick").should("have.been.calledOnce"); }); });

CI Patterns

Artifacts (videos/screenshots)

Store artifacts for failed runs and keep videos optional to reduce storage.

// cypress.config.ts import { defineConfig } from "cypress";

export default defineConfig({ video: false, screenshotOnRunFailure: true, retries: { runMode: 2, openMode: 0 }, });

Parallelization (Cypress Cloud)

Parallelize long E2E suites via Cypress Cloud when runtime dominates feedback loops.

Anti-Patterns

• Use cy.wait(1000) as a synchronization mechanism.

• Select elements via deep CSS paths.

• Mix heavy network stubbing with “real backend” assertions in the same spec.

• Depend on test order; isolate state with cy.session and per-test setup.

Troubleshooting

Symptom: flaky click or element not found

Actions:

• Add a data-testid hook for the element.

• Assert visibility before interaction (should("be.visible") ).

• Wait on network alias for the data that renders the element.

Symptom: tests fail only in CI

Actions:

• Increase run-mode retries and record screenshots on failure.

• Verify viewport and baseUrl config match CI environment.

• Eliminate reliance on local-only seed data; create data via API calls.

Resources

• Cypress docs: https://docs.cypress.io/

• Best practices: https://docs.cypress.io/guides/references/best-practices