Write Tests

Overview

Write tests that prove behavior with the smallest useful fixture surface. Use Remix's own test/assert packages and describe/it style by default, keep package dependency graphs clean, and validate with the narrowest reliable commands.

Workflow

1. Read the nearest package.json, tsconfig.json, and existing sibling tests before choosing a runner or fixture style.
2. Identify whether the package can depend on @remix-run/test, or whether it is a dependency of @remix-run/test and must avoid a circular dependency.
3. Keep the test close to the behavior owner. Prefer local helpers and direct Web/Node primitives over importing higher-level workspace packages as fixtures.
4. Put test-only workspace packages in devDependencies with workspace:^; do not add them to runtime dependencies.
5. Run the package test and typecheck commands. Refresh pnpm-lock.yaml when package metadata changes.

Runner Choice

• Write new and changed tests in describe/it style. When touching a file that uses top-level test(), convert the affected tests to describe/it and leave unrelated tests alone.
• Use @remix-run/test and @remix-run/assert by default for package tests.
• Use node:test and node:assert/strict only when testing a package that is a dependency of @remix-run/test, or when adding Remix test/assert as a dependency would create a circular dependency.
• Do not keep a test:bun script for node:test packages unless it has been validated. Bun's test runner does not automatically discover tests written with node:test imports.

Node test package script:

"test": "node --disable-warning=ExperimentalWarning --test './src/**/*.test.ts'"

Node test imports:

import * as assert from 'node:assert/strict'
import { describe, it } from 'node:test'

Remix test package script:

"test": "remix test"

Remix test imports:

import * as assert from '@remix-run/assert'
import { describe, it } from '@remix-run/test'

Test Structure

• Name describe() blocks after the public API or behavior owner, and name it() tests by observable behavior.
• Do not generate tests inside describe() with loops or conditionals; this breaks per-test IDE execution.
• Prefer a few explicit cases over dense table tests when the cases document distinct behavior.
• Keep async tests awaited all the way through. Avoid resolving promises before the behavior under test has completed.
• Use mocks sparingly and locally. Prefer the Remix test context mocks when using @remix-run/test; use mock.method()/mock.fn() from node:test only in node-runner exception packages.

Fixtures

• Keep fixtures minimal and local to the test file unless they are reused across multiple files for the same behavior surface.
• Avoid importing higher-level workspace packages just to build a fixture. For example, a fetch-handler test can branch on new URL(request.url).pathname instead of depending on @remix-run/fetch-router.
• Prefer Web APIs and standards-aligned primitives when they express the fixture clearly.
• For e2e tests, serve the smallest app or handler that exercises the user-observable behavior under test.
• For HMR tests, use real file changes, child processes, watchers, and browser assertions when the public behavior depends on runtime coordination.
• Close spawned processes, asset servers, watchers, and HTTP servers in test cleanup.

Assertions

• Use @remix-run/assert by default.
• Use node:assert/strict only in node-runner exception packages that cannot depend on @remix-run/assert/@remix-run/test.
• Assert public behavior and observable side effects. Avoid asserting private implementation structure unless the package's public contract is the structure.
• For error tests, assert the error shape/message that consumers can rely on.

Dependency Hygiene

• Runtime code imports belong in dependencies.
• Test files, fixtures, and runner-only imports belong in devDependencies.
• Use workspace:^ for workspace package dependencies unless the repo has an established reason for workspace:*.
• After changing package dependencies or scripts, run pnpm i --lockfile-only --ignore-scripts and then a frozen install check.
• Reassess workspace cycles when changing testing infrastructure: pnpm i --frozen-lockfile --ignore-scripts should not emit cyclic workspace dependency warnings.

Validation

Use the narrowest meaningful commands:

pnpm --filter @remix-run/<package> run test
pnpm --filter @remix-run/<package> run typecheck
pnpm i --frozen-lockfile --ignore-scripts

For cross-package or shared test infrastructure changes, also consider:

pnpm run test:changed
pnpm run typecheck:changed
pnpm run lint