Redis Connections closing in Heroku CI using heroku-redis:in-dyno - node.js

Question

Tests run (and Redis works) perfectly fine in a local environment
Redis works normally even when deployed to production
However Redis connections immediately close when run in Heroku's CI test environment
Technologies used:
Node.js, Express, Mocha, Chai, Supertest
Heroku, Heroku CI, (Heroku) Redis
I'm having the tests run through the Pipeline feature. And then I get the following error output:
-----> Running test command `make test-ci`...
NODE_ENV=test ./node_modules/.bin/db-migrate up --log-level=error --env=test --config=config/database.json --migrations-dir ./db/migrations
NODE_ENV=test ./node_modules/.bin/mocha --exit --ui bdd --reporter spec --timeout 15000 --recursive ./tests/setup.js ./tests/
Redis successfully connected
POST: API /account/phone
Redis set error The client is closed
1) accepts a phone number and generates a PIN
0 passing (15s)
1 failing
1) POST: API /account/phone
accepts a phone number and generates a PIN:
Error: Timeout of 15000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/app/tests/api/account.js)
make: *** [Makefile:66: test-ci] Error 1
-----> test command `make test-ci` failed with exit status 2
My app.json file looks like this
{
"environments": {
"test": {
"scripts": {
"test": "make test-ci"
},
"addons": [
"heroku-redis:in-dyno",
"heroku-postgresql:in-dyno"
]
}
}
}
My Redis connection file looks like this:
let redis = require('redis')
let client = redis.createClient({
url: process.env.REDIS_URL
})
client.on('error', err => console.log('Redis Client Error', err))
client.on('connect', () => {
console.log('Redis successfully connected')
})
The route that's being tested looks like this:
redis.set('phone:keys:' + phone, code, { EX: 60 * 5 }).then(val => {
console.log('did it get set in redis?')
twilio.send(phone, message).then(response => {
res.status(201).json({
ok: true,
data: { body: response.body },
})
})
})
.catch((err) => {
console.log('Redis set error', err.message)
})
In local env (and production), it all works normally. Even when running tests locally. But only in Heroku CI it fails, and I see the "Redis set error The client is closed "