@jeanlauliac mentioned it would be great if Jest could come with a kick-ass fs mock out of the box.
- This would work well for integration tests.
- We can potentially provide the same for other data sources (http, sockets etc.)
Goal:
- Ships as part of Jest, no configuration.
- Easy way to enable it (Similar to
jest.mock('fs')?).
cpojer
All 23 comments
I was thinking about the same thing, this would be great! FS and HTTP requests sound like a great idea
rogeliog
on 16 Mar 2017
Yes please! As someone who has recently starting with Unit Testing and TDD you guys have made the experience super simple without sacrificing utility. Now that I'm trying to test some related stuff with fs It's starting to become quite complex. Props to you guys for all the work!
cesalberca
on 8 May 2017
Can you explain better what do you guys want to? :)
unsidez
on 16 May 2017
I think it would be a fully fleshed out implementation of the "fs" library, but built entirely around mocking and stubbing. An example would be how VCR does that for XMLHttpRequest, but for file system access.
There's a few ways it could be done. Perhaps you could provide a dummy "fs" module that lets you use an external API for your files, or you could provide an object of files and reference data (I do this in Forgeries )
orta
on 16 May 2017
@ide has a proposal for this!
cpojer
on 16 May 2017
In my mind, it'd be great to just have a simple mock API where using fs.writeFile writes to a pure memory filesytem instead of disk, and where fs.readFile allows to read files that have been written as such. Of course everything else would also work on that memory fs, such as fs.createReadStream, fs.open, fs.watch, etc. In practice, tests could write necessary files in beforeEach, call the code to be tested, and possibly verify content of files afterwards.
fs.mockMemoryFS('posix');
const fs = require('fs');
const smth = require('../smth');
it('works', () => {
fs.writeFileSync('/var/test_file', 'foo');
smth('/var/test_file');
expect(fs.readFileSync('/var/test_file', 'utf8')).toMatchSnapshot();
});
We could imagine supporting explicitely posix/win environment no matter the real host OS, and having the mock automatically create traditional posix directories such as /tmp.
(As for sockets/HTTP, that'd be amazing to be able to create a completely virtual network of machines and being able to test client/server interactions, etc.)
jeanlauliac
on 16 May 2017
Any updates in this one?
digitalkaoz
on 2 Dec 2017
Yes please. I've had many issues trying to get mock-fs to play nice with jest.mock. Having it built-in would be great.
milesj
on 2 Dec 2017
There is https://github.com/webpack/memory-fs. I haven't actually tested if sticking it in __mocks__/fs is enough.
SimenB
on 2 Dec 2017
We have a pretty good mock here: https://github.com/facebook/metro/blob/master/packages/metro/src/node-haste/__mocks__/fs.js but never had any chance to polish it and pull it out.
cpojer
on 2 Dec 2017
The one you mentioned @cpojer lacks many features and has a lot of problems to be fixed; though that was indeed the one I was thinking of reusing after improvements. memory-fs is worth investigating, as it looks feature-complete!
jeanlauliac
on 2 Dec 2017
Will it allow me to just Mock parts of the Filesystem and leave the rest
untouched? Primarly i just want to mock a folder and a few files, leaving
the rest untouched. So require works as normal and so on...trying to get
spyfs+memfs to work. But it doesnt seem as easy as i thought...
Jean Lauliac notifications@github.com schrieb am Sa., 2. Dez. 2017, 12:07:
The one you mentioned @cpojer https://github.com/cpojer lacks many
features and has a lot of problems to be fixed. memory-fs looks worth
investigating! ^_^—
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digitalkaoz
on 2 Dec 2017
Will it allow me to just Mock parts of the Filesystem and leave the rest untouched? Primarly i just want to mock a folder and a few files, leaving the rest untouched. So require works as normal and so on...trying to get spyfs+memfs to work. But it doesnt seem as easy as i thought...
I think it's an all or nothing thing. But I think it'll behave like you want, as jest implements require itself, so those would dodge the mocked fs anyways. I'd be curious to hear experiences using memory-fs for tests.
It's under the hood of webpack-dev-server, so pretty well tested. Would be cool if we could just point to it
SimenB
on 2 Dec 2017
I've started working on building a high-quality memory FS, I think I'll send a PR sometime next week.
I've looked at the memory-fs package but it doesn't implement the path resolution behaviour as it happens on Linux/BSDs-type machines (that is what I'm targeting as a first step), especially when it comes to symlinks. It is also missing a bunch of pieces of functionality (ex open, lstat, etc.), contrary to what I thought at first.
(A realistic memory FS for Windows might need some adjustments, but that's for later.)
jeanlauliac
on 14 Dec 2017
@jeanlauliac i played around with https://github.com/streamich/spyfs and https://github.com/streamich/memfs it was the most promising variant for me.
it did it by spying on the realfs and only intercepting stuff thats defined in the memfs volume...
it worked 98%. if you are interested i can share some code. all other variants failed for one or another reason
digitalkaoz
on 15 Dec 2017
@jeanlauliac, @digitalkaoz, @cpojer: Any updates?
Alternatively, it would be great if anyone could share their own fs mocks in the meantime.
b0o
on 2 Apr 2018
We use metro-memory-fs at the moment for Metro's automated tests, that has proper path resolutions and a few of the core functions we needed. It lacks docs, but it's essentially the same API as fs. It can be used as as such:
jest.mock('fs', () => new (require('metro-memory-fs'))());
beforeEach(() => require('fs').reset()); // optional, cleans up the whole filesystem
It has fairly decent test coverage itself, so contributions are welcome!
jeanlauliac
on 3 Apr 2018
Do we still think this should be shipped as part of Jest?
SimenB
on 3 Feb 2019
A mock file system would be nice if Jest ever had first class support for fixtures.
milesj
on 3 Feb 2019
The Metro one is great. Use metro-memory-fs. It doesn't need to be part of Jest.
cpojer
on 4 Feb 2019
it needs to support require('fs').promises; though 😀
SimenB
on 4 Feb 2019
Pull Requests welcome!
cpojer
on 4 Feb 2019
SimenB
on 4 Feb 2019
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Most helpful comment
We use
metro-memory-fsat the moment for Metro's automated tests, that has proper path resolutions and a few of the core functions we needed. It lacks docs, but it's essentially the same API asfs. It can be used as as such:It has fairly decent test coverage itself, so contributions are welcome!