I am creating a JS test on my react-native project. I'm specifically using firebase for react native, in which I would like to replace firebase instance with a mockfirebase instance if JS is running the code of my class.
For example I have class setup like below.
import firebase from 'react-native-firebase';
class Database() {
/// use the firebase instance
}
I'd like to have a check if jest is the running environment then I'd replace the import line with appropriate mock class.
jest sets an environment variable called JEST_WORKER_ID so you check if this is set:
function areWeTestingWithJest() {
return process.env.JEST_WORKER_ID !== undefined;
}
I also see that if NODE_ENV is not set the jest CLI sets it to the value 'test'. This might be another way to check.
JEST_WORKER_ID will defined in production too since it seems to use jest-worker module for it.
process.env.JEST_WORKER_ID === undefined || process.env.NODE_ENV !== 'test'I usually have NODE_ENV=development set globally on my shell. This works for me:
typeof jest !== 'undefined'
(note that global.jest and 'jest' in global don't work, as this doesn't seem to be a global variable, just a value made available on all modules much like node's require or __filename)
typeof jest !== 'undefined' is false (i.e. it is defined) when running in the iOS simulator, attached to the debugger, so I had to check the worker ID as shown in the other answer.you could add parameter to global for example global.isJest and check on the front end if it is defined
For me best way is checking two things - 0 and undefined:
[0, undefined].includes(process.env.JEST_WORKER_ID)
so it's based on https://stackoverflow.com/a/52231746/3012785
includes method because expectations are different since the left is a combination of [string and number], but the other side is globally considered a string.
