Jest did not exit one second after the test run has completed

Jest did not exit one second after the test run has completed.

This usually means that there are asynchronous operations that weren't stopped in your tests. Consider running Jest with `--detectOpenHandles` to troubleshoot this issue.

포트를 여는 코드(listen)가 포함된 파일을 테스트할 경우 생기는 에러이다. 포트를 분리 시켜주고, 다시 테스트를 하면 에러가 사라진다.