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.
このようなエラーがでた。
原因はポートが開きっぱなしになってしまうこと。
app.jsを分割。testを非同期にすることで解決