I removed the res.send for each of the testConnection method calls, and added the following lines at the end.
const successful = new Promise(() =>{
logger.info("Completed connection tests")
})
res.send(successful)
This way it only sends a single promise after the tests are successful.
My connector tests are now passing again. I think the issue was that previously I was returning a single res.send, and then I changed my code to look at multiple connections which returned multiple res.send.