Have tested numerous times and coverage is never written when I do ember t, it is only written when I do ember t -s. This doesnt play well with the CI jobs of course. I do use embroider.

On the current versions of almost all addons. Have checked the docs and have the babel plugin correct, have the ember-concurrency plugin before it. Using mirage, have the /write-coverage in the correct place, etc. I believe I have it configured correctly because I do get coverage, just have to specify -s.

Anyone got any idea on what could be the issue?

I do notice that when I run tests, I get the following error which to me looks like it is attempting an http request (assuming attempting to write coverage)

BadRequestError: request aborted
    at IncomingMessage.onAborted (/Users/brian.gantzler/source/rxid/ember/ember-rxid/node_modules/raw-body/index.js:245:10)
    at IncomingMessage.emit (node:events:520:28)
    at IncomingMessage._destroy (node:_http_incoming:224:10)
    at _destroy (node:internal/streams/destroy:122:10)
    at IncomingMessage.destroy (node:internal/streams/destroy:84:5)
    at abortIncoming (node:_http_server:806:9)
    at socketOnClose (node:_http_server:800:3)
    at Socket.emit (node:events:532:35)
    at TCP.<anonymous> (node:net:338:12)