CORS error - Error: Cross origin http://localhost forbidden - in ReactJS/Jest test only - reactjs

Question

I'm running into a problem where the request I am making to an outside API is working fine in execution, but when runing a Jest/Enzyme test it gives me a CORS error. The function in question is using a JsonRpc implementation from an API, and using fetch from node-fetch. Not sure if there are settings for CORS I can apply somewhere?
I tried many variations of async waits in Jest/Enzyme testing framework but am still running into issues.
test("it should do something", done => {
const component = shallow(<CustomComponent />)
component.instance().customAsyncFunction( result => {
expect(result.length).toEqual(5)
done()
})
// return component.instance().customAsyncFunction().then(data => {
// expect(data.length).toEqual(5)
// })
})
I tried the above and a few other methods (like setTimeout and awaiting it) and get the CORS error.
The results I'm getting are:
console.error
node_modules/jest-environment-jsdom/node_modules/jsdom/lib/jsdom/virtual-console.js:29
Error: Cross origin http://localhost forbidden
at dispatchError (...\node_modules\jest-environment-jsdom\node_modules\jsdom\lib\jsdom\living\xhr-utils.js:65:19)
at Request.client.on.res (...\node_modules\jest-environment-jsdom\node_modules\jsdom\lib\jsdom\living\xmlhttprequest.js:679:38)
at Request.emit (events.js:198:13)
at Request.onRequestResponse (...\node_modules\request\request.js:1066:10)
at ClientRequest.emit (events.js:203:15)
at HTTPParser.parserOnIncomingClient [as onIncoming] (_http_client.js:556:21)
at HTTPParser.parserOnHeadersComplete (_http_common.js:109:17)
at TLSSocket.socketOnData (_http_client.js:442:20) undefined
Any ideas?

Answer 1

Jest allows you to set a setup script file. This file will be required before everything else and gives you a chance to modify the environment in which the tests will run. This way you can unset XMLHttpRequest before axios is loaded and the adapter type evaluated since imports are hoisted.
Link:https://facebook.github.io/jest/docs/configuration.html#setuptestframeworkscriptfile-string
In package.json
{
...,
"jest": {
...,
"setupTestFrameworkScriptFile": "./__tests__/setup.js",
...
},
...
}
__tests__/setup.js
global.XMLHttpRequest = undefined;

Answer 2

The error happens because the external API you call during the tests has a CORS restriction different than Jest's default jsdom one has (http://localhost).
To fix this for Jest v24 - v27 you have to set the appropriate testURL (see the docs) in your Jest config (e.g. jest.config.js):
{
// Other config values here ...
"testURL": "http://localhost:8080"
}
In testURL you have to put the actual URL allowed by CORS at your remote API side.
NB: since v28 the option is organized differentlty that requires different update in Jest config.

Answer 3

Assuming you actually want to call the real API during your tests rather than just mock it, you'll need to make sure the server sends an appropriate "access-control-allow-origin" header (obviously the exact mechanism for doing this depends on your server platform)

Answer 4

1) what you're probably looking for is to instead mock the promise or whatever function is being ran using jest.mock(), then assert that that mock was called (with the correct params)
Jest tests are unit tests that shouldn't really talk to your API
2) most likely something with your env vars while in test mode, process.env.NODE_ENV is set to "test" during jest which might be changing something or maybe one of your own custom config env vars

Answer 5

By settting a testURL option which is a valid URL you want in jest config will resovle this problem.
https://jestjs.io/docs/configuration#testurl-string