Vitest Memfs

Project Overview

vitest-memfs adds a set of memfs-aware matchers to Vitest, enabling file-heavy integration tests to run in memory while using Vitest’s regular expect API.

Why

I often build tooling (bundlers, project scaffolds, CLIs) that pipes files through memfs to avoid touching the real disk. Assertions turned into hand-written vol.existsSync checks and fragile object diffs. The package extracts the helpers I rewrote across projects into a reusable set of matchers with tight TypeScript support, glob awareness, and snapshot integration.

Key Matchers

• toHaveVolumeEntries — assert that exact paths or glob patterns exist in a volume, optionally verifying the entry type (file, dir, symlink) or an expected count.
• toMatchVolume — compare an in-memory volume against another volume or JSON tree with support for prefix, ignore, and directory list matching modes (exact, ignore-extra, ignore-missing).
• toMatchVolumeSnapshot — persist a snapshot of a volume to disk (under __snapshots__/) and diff future runs; supports async comparison, glob ignores, and throttled concurrency for large trees.

All matchers share a consistent options object (prefix, ignore, listMatch, contentMatch, report, async, concurrency) so tests can zoom in on the interesting slice of the filesystem without noise.

Tooling Notes

• Written in TypeScript, bundled with pkgroll, and built for Node 18+ in both ESM and CJS formats.
• CI runs Vitest on both Linux and Windows to ensure cross-platform compatibility, collects coverage with V8 + Codecov, and handles automated releases through Semantic Release.
• Exposes a setup entry (vitest-memfs/setup) plus matcher and utility subpaths exports.

Check out the project repository on Github for more info.