test-fs

A tiny filesystem helper test library that creates actual files.

• it does not mock / interfere with existing modules;
• it just creates plain text files for tree structure test purposes.

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Install

npm install @moonwave99/test-fs -D

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Examples

See on Stackblitz

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Docs

testFs(tree: Tree = {}, context: string = ")

Creates the passed tree in the tmp folder. If a context value is passed, it creates it inside the {context} subfolder.

Note: object values are folders, strings are files. Object keys are names.

import { testFs } from "@moonwave99/test-fs";

const rootDir = await testFs({
  emptyFolder: {},
  folder: {
    nested: {
      "file.txt": "some content",
    },
    "empty-file.txt": "",
  },
});

It creates:

{rootDir}
  emptyFolder
  folder
    nested
      file.txt
    empty-file.txt

You can also pass complete paths as values:

import { testFs } from "@moonwave99/test-fs";

const rootDir = await testFs({
  "path/to/file-1.txt": "",
  "path/to/file-2.txt": "",
});

It creates:

{rootDir}
  path
    to
      file-1.txt
      file-2.txt

testFsCleanup(context: string = ")

Cleans the passed directory. If context is passed, it cleans the {context} subfolder.

Be sure to know what you are passing!

import { testFs, testFsCleanup } from "@moonwave99/test-fs";

const rootDir = await testFs(
  {
    emptyFolder: {},
    folder: {
      nested: {
        "file.txt": "some content",
      },
      "empty-file.txt": "",
    },
  },
  "your-context-id"
);

// some operations

await testFsCleanup("your-context-id");

Add the following to your main test configuration (e.g. vitest.setup.ts or similar):

// get a fresh tmp context every time
beforeEach( (context) => testFsCleanup(context.task.id));

// clean the whole tmp folder after done
afterAll(() => testFsCleanup());

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Rationale

I faced some issues with the in-memory/mock libraries, so I decided to sacrifice a little performance in order to work with actual files and folders.

Since test runners like Jest expose an unique context.task.id value, it's easy to create independent temporary folders where to check for the expected output, for instance:

describe('saveNote function', () => {
  it('saves a note for the corresponding user', async (context) => {
    // creates an empty folder
    const dataFolder = await testFs({}, context.id);

    const noteId = await saveNote({
      userId: 1,
      content: 'Some text',
      dataFolder,
    });

    const outputPath = path.join(dataFolder, '1', `note-${noteId}.txt`);

    expect(await fs.exists(outputPath)).toBe(true);
    expect(await fs.readFile(outputPath, 'utf8')).toBe('Some text');
  });
});

describe('readNote function', () => {
  it('reads the contents for the corresponding note', async (context) => {
    // it populates the folder with some content, without needing call saveNote first
    const dataFolder = await testFs(
      {
        1: {
          'note-123.txt': 'Some content',
        },
      },
      context.id
    );

    const contents = await readNote({
      userId: 1,
      noteId: 123,
      dataFolder,
    });

    expect(contents).toBe('Some content');
  });
});

The tests can thus safely run in parallel.

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License

ISC License

Copyright 2025 Diego Caponera

Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.