Jest breaks Buffer instanceof Uint8Array

[dignifiedquire]

Do you want to request a feature or report a bug?
Bug

What is the current behavior?

In nodejs (8.4.0)

new Buffer('hello') instanceof Uint8Array
// => true

In jest (21.0.1)

new Buffer('hello') instanceof Uint8Array
// => false
new Buffer('hello').buffer instanceof Uint8Array
// => false

This breaks quite a few modules that assume (as they should be able to) that node buffers are Uint8Arrays.

[dignifiedquire]

Update, tried setting testEnvironment: node explicitly, still the same issue

[dignifiedquire]

The issue is that jest-util doesn't pass all necessary globals through.

[cpojer]

This is unfortunately a side-effect of Jest pulling in the node libraries from the parent context, but having its own instances of UInt8Array in the child contexts. One thing you could try is to create your own environment that runs all tests in the main process, or overwrites UInt8Array in the child context with the one in the parent context. We don't have a good fix for this yet.

[dignifiedquire]

Passing more globals through to the child process works in my tests, see #4423. Currently I am not seeing a big drawback to doing that, except that that list needs to be maintained. But I might be missing some context there.

[dignifiedquire]

We cannot pull these globals from the parent context into the vm contexts unfortunately

Why the requirement of having the parent Buffer but the child globals for things like Uint8Array?

[cpojer]

This is not expected, it is a bug, but because Jest tries to keep individual tests sandboxes and isolated, we cannot leak more things into the vm. Ideally we wrap all core libraries so that we swap out the prototypes later, like myBuffer.__protot__ = Uint8Array or re-evaluate all of node's core library code inside the vm context, but pulling them in from the parent is unfortunately not the right general solution. Using your own test environment should provide an escape hatch for you that should work reasonably well, as long as you know about the trade offs.

[dignifiedquire]

Using your own test environment should provide an escape hatch for you that should work reasonably well, as long as you know about the trade offs.

Makes sense, thank you 👍

[dignifiedquire]

Custom environment works like a charm, for anyone coming here I created this: https://github.com/ipfs/jest-environment-aegir

[cpojer]

Thanks for working on this env and sharing it with everybody :) I'll close this issue as I know it's tracked somewhere on our issue tracker but I can't find it right now :( I'm sure somebody in the future will reference the two together.

[valamidev]

As a possible solution:

expect(Object.prototype.toString.call(new Uint8Array()).toEqual('[object Uint8Array]'); // PASS

[kevincox]

This should probably be reopened or a link to the other tracking issue should be found.

[kevincox]

The fix is to create a jest.config.js with the following. (Example)

export default {
	globals: {
		Uint8Array: Uint8Array,
	},
};

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