component-testing

Component Testing

Vitest Browser Mode with Playwright. Tests run in real Chromium — every DOM API, CSS layout, and browser behavior is authentic.

Conventions

• Co-locate tests: foo.browser.test.tsx next to foo.tsx
• Always wrap in describe named after the component
• Use test, not it
• render() is async — always await it
• Test behavior through rendered output, not implementation details
• Do NOT test shadcn/ui primitives — only test your own components that compose them

describe("SearchFilter", () => {
  test("filters results on input change", async () => { ... });
  test("shows empty state when no matches", async () => { ... });
});

When to Test

Test when a component has:

• useState or state management logic
• useEffect or side effects
• Event handlers with conditional logic
• Conditional rendering based on props or state
• Complex prop transformations

Skip when a component:

• Is a pure style wrapper (just applies CSS classes)
• Has no logic — only passes props through
• Is a thin layout component
• Is a shadcn/ui primitive

Vitest Browser API

import { render } from "vitest-browser-react";
import { page } from "vitest/browser";
import { describe, expect, test, vi } from "vitest";

API	Use
await render(<C />)	Mount component
page.getByRole("button", { name })	Query by ARIA role
page.getByText("text")	Query by text content
page.getByLabelText("label")	Query by label
locator.click()	Click interaction
locator.fill("value")	Type into input
await expect.element(locator)	Auto-retry assertion (1s)
expect(value)	Synchronous assertion

expect.element() vs expect()

Use	When
await expect.element(locator)	Page locator queries — auto-retries until pass
expect(value)	Mock assertions, container.querySelector(), non-DOM values

What NOT to Test

• CSS classes — test visible behavior instead
• Internal state — verify through rendered output
• Implementation details — don't test hook call order

Examples

See examples/ for complete test examples by pattern:

Example	When to use
examples/render-and-query.md	Basic rendering, role and text queries
examples/user-interactions.md	Clicks, toggles, stateful interactions
examples/form-testing.md	Form inputs, submission, validation
examples/conditional-rendering.md	Show/hide content based on props or state
examples/container-queries.md	DOM structure, data-* attributes, container.querySelector()
examples/compound-components.md	Multi-part composed components

Acceptance Checklist

• Test file uses .browser.test.tsx extension
• Co-located next to the component
• Wrapped in describe named after the component
• Uses test, not it
• render() is awaited
• Uses expect.element() for locator assertions
• Tests behavior, not implementation details
• Mocks only at system boundaries