Mocha before function not working correctly - node.js

Question

I'm trying to read a csv file in my before hook but it's getting executed after the test itself for some reason.
let csvPath = path.join(__dirname, '/sample-conv.csv')
let messages = []
// read csv and push rows into an array
before(done => {
fs.createReadStream(csvPath).pipe(csv.parse({ headers: true })).on('data', row => {
messages.push(row)
}).on('end', () => {
console.log('before', messages) // this logs the full array correctly
done()
})
})
describe('Should return correct responses', () => {
let hardCoded = ['Hi', 'This is a response'] // hard codes responses to stub chatbot
console.log('after', messages) // logs empty array
it('dummy', done => {
expect(true).eq(true);
done()
})
// messages.forEach((row, i) => {
// it('Should return expected response for message #' + (i + 1), done => {
// const { send, expected } = row
// let actual = hardCoded[i]
// expect(actual).to.equal(expected)
// done()
// })
// })
})
There's also the issue that the commented out it function is not executed at all. I added the dummy test just to try to fix the before issue first. I'm assuming it's not working because of the loop.

Answer 1

mocha RUN CYCLE OVERVIEW
:
When a test file is loaded, Mocha executes all of its suites and finds–but does not execute–any hooks and tests therein.
Any “before all” hooks (for the root suite, this only happens once; see root hook plugins)
Every call to describe() immediately executes its callback. However, calls to it record the test for later execution. Mocha is discovering your tests while doing this but not executing them right away. At this point in time, the before hook has not been executed. That's why console.log('after', messages) logs empty array.
Simply put, the order of execution is: describe() and its callback => before hook => it()
E.g.
const { expect } = require('chai');
let messages = [];
before((done) => {
// simulate read csv operator
setTimeout(() => {
messages.push(...[1, 2, 3]);
console.log(`[${new Date().toISOString()}] before`, messages);
done();
}, 1000);
});
describe('Should return correct responses', () => {
console.log(`[${new Date().toISOString()}] after`, messages);
it('dummy', () => {
console.log(`[${new Date().toISOString()}] run dummy test case`);
expect(messages).to.be.deep.eq([1, 2, 3]);
});
});
test result:
[2020-12-25T05:31:45.066Z] after []
[2020-12-25T05:31:46.073Z] before [ 1, 2, 3 ]
Should return correct responses
[2020-12-25T05:31:46.075Z] run dummy test case
✓ dummy
1 passing (1s)