Short one. If `bun run test` is failing with `vitest: command not found` even though vitest is clearly in your `devDependencies`, read on.

## What's Happening

Your `package.json` probably looks like this:

```json
{
  "scripts": {
    "test": "vitest run"
  }
}
```

When npm or pnpm runs a script, they prepend `node_modules/.bin` to `PATH` before executing. That's how `vitest run` resolves to the locally installed binary.

Bun does this too — *most of the time*. But the behavior isn't always consistent across Bun versions, shell environments, and CI setups. In some contexts (Docker images, certain CI runners, non-interactive shells), `node_modules/.bin` doesn't make it onto `PATH`, and Bun falls back to the system shell which has no idea what `vitest` is.

## The Fix

Replace the bare binary name with `bunx`:

```json
{
  "scripts": {
    "test": "bunx vitest run",
    "test:watch": "bunx vitest",
    "test:coverage": "bunx vitest run --coverage"
  }
}
```

`bunx` is Bun's package runner — equivalent to `npx` for npm or `pnpx` for pnpm. It resolves and executes the binary from `node_modules/.bin` explicitly, regardless of what's on `PATH`. No ambiguity, no environment dependency.

## Why Not Just Install Vitest Globally?

You could — `bun add -g vitest` — but then you've introduced a version dependency on whatever global is installed on each machine. Your CI passes with vitest 3.x, someone runs it locally with vitest 4.x, tests behave differently. `bunx` always uses the version from the project's `node_modules`, which is pinned in `bun.lockb`.

## Why Not Hardcode the Path?

```json
"test": "bun node_modules/.bin/vitest run"
```

This works but it's fragile. The path separator is platform-specific, and it'll break in any project where `node_modules` lives somewhere other than the project root (monorepos, workspaces). `bunx` handles all of that for you.

## The Pattern

For any CLI tool you run in `package.json` scripts under Bun, prefer `bunx <tool>` over bare `<tool>`. It's explicit, portable, and always resolves from the local install:

```json
{
  "scripts": {
    "test": "bunx vitest run",
    "lint": "bunx biome check .",
    "typecheck": "bunx tsc --noEmit"
  }
}
```

The only exception is scripts that are Bun builtins or shell commands — those don't go through `bunx`.