Easier way to use memfs in tests

I’m trying to use memfs in tests. Use case is like this:

1. Mock fs with memfs:

   // __mocks__/fs.js
   process.chdir('/');
   module.exports = require('memfs').fs;
   

2. Load the initial state from JSON using fromJSON method.

3. Run methods I’m testing.

4. Inspect the resulting JSON from toJSON.

The problem is that every time I call fromJSON it modifies the volume, keeping all existing files from previous tests.

I see two possible solutions:

1. Recreate a memfs volume before each test. Seems a bit too complex.
2. rm -rf / after each tests. But it seems scary — what if I forget to call jest.mock('fs')? ;-|

As a perfect solution I see fromJSON that can remove all existing files before loading JSON. Could be a new parameter or a new method.

What do you think?

[sapegin]

I’m trying .reset() and test cases look really nice:

jest.mock('fs');

const { vol } = require('memfs');
const { copyFiles } = require('../fs');

afterEach(vol.reset.bind(vol));

describe('copyFiles()', () => {
	it('should copy a file', () => {
		vol.fromJSON({ 'tmpl/a': 'pizza' });

		copyFiles('tmpl', 'a');

		expect(vol.toJSON()).toMatchSnapshot();
	});

	it.skip('should copy multiple files', () => {
		vol.fromJSON({ 'tmpl/a': 'pizza', 'tmpl/b': 'coffee' });

		copyFiles('tmpl', ['a', 'b']);

		expect(vol.toJSON()).toMatchSnapshot();
	});

	it.skip('should not overwrite a file if  overwrite=false', () => {
		const json = { 'tmpl/a': 'pizza', a: 'pizza' };
		vol.fromJSON(json);

		copyFiles('tmpl', 'a', { overwrite: false });

		expect(vol.toJSON()).toEqual(json);
	});
});

[streamich]

I like the .toJSON() with .toMatchSnapshot().