fs-fixture

name	fs-fixture
description	Create disposable file system test fixtures from objects, templates, or empty directories with automatic cleanup. Use when writing tests that need temporary files, directories, symlinks, or JSON fixtures on disk. Keywords - fs, tmp, temp, fixture, testing utility, cleanup, dispose.

Quick Start

import { createFixture } from 'fs-fixture'

// From object — keys are paths, values are content
const fixture = await createFixture({
    'package.json': JSON.stringify({ name: 'test' }),
    'src/index.js': 'export default 42',
})

// Use fixture.path, fixture.readFile(), etc.
await fixture.rm() // Cleanup when done

Auto-cleanup with using (TypeScript 5.2+):

await using fixture = await createFixture({ 'file.txt': 'content' })
// Automatically cleaned up when scope exits

createFixture(source?, options?)

Source	Behavior
{ path: content }	Create files from object. Nested objects create directories.
'./path'	Copy template directory into fixture
(omitted)	Empty temporary directory

Option	Type	Default	Description
tempDir	string | URL	os.tmpdir()	Custom parent directory
templateFilter	(src, dest) => boolean	—	Filter files when copying template

FsFixture Methods

Method	Description
fixture.path	Absolute path to fixture root
getPath(...paths)	Resolve path relative to fixture root
exists(path?)	Check existence (returns boolean)
readFile(path, encoding?)	Read file — 'utf8' returns string, omit for Buffer
writeFile(path, content)	Write string or Buffer
readJson<T>(path)	Read and parse JSON with type parameter
writeJson(path, data, space?)	Write JSON (default: 2-space indent, 0 for minified)
readdir(path, options?)	List directory ({ withFileTypes: true } for Dirent[])
mkdir(path)	Create directory recursively
cp(source, dest?)	Copy external file/directory into fixture
mv(source, dest)	Move or rename within fixture
rm(path?)	Delete path, or entire fixture if omitted

FileTree Values

Type	Example
string	'file content'
Buffer	Buffer.from([0x89, 0x50])
Nested object	{ dir: { 'file.txt': 'content' } }
Function	({ fixturePath, filePath, getPath, symlink }) => symlink('./target')

Path syntax — these are equivalent:

// Nested objects
{ src: { utils: { 'helper.js': 'code' } } }

// Slash-separated keys
{ 'src/utils/helper.js': 'code' }

[!TIP] Slash-separated keys can also group a shared prefix:

await createFixture({
    'file.js': 'import { a } from "my-pkg";',

    'node_modules/my-pkg': {
        'package.json': JSON.stringify({
            name: 'my-pkg',
            type: 'module',
            exports: './index.js'
        }),
        'index.js': 'export const a = 1;'
    }
})

Patterns

Symlinks

const fixture = await createFixture({
    'target.txt': 'real file',
    'link.txt': ({ symlink }) => symlink('./target.txt'),
    'node_modules/pkg': ({ symlink }) => symlink(process.cwd()),
})

Dynamic content

const fixture = await createFixture({
    'info.txt': ({ fixturePath }) => `Root: ${fixturePath}`,
})

Related

Commonly used with manten test framework.