The test is very sensitive to how backends start and exit, because it tests dead-end backends which occur when all the connection slots are in use. The test failed occasionally in the CI, when the backend that was launched for the raw_connect_works() check lingered for a while, and exited only later during the test. When it exited, it released a connection slot, when the test expected all the slots to be in use at that time. The 002_connection_limits.pl test had a similar issue: if the backend launched for safe_psql() in the test initialization lingers around, it uses up a connection slot during the test, messing up the test's connection counting. I haven't seen that in the CI, but when I added a "sleep(1);" to proc_exit(), the test failed. To make the tests more robust, restart the server to ensure that the lingering backends doesn't interfere with the later test steps. In the passing, fix a bogus test name. Report and analysis by Jelte Fennema-Nio, Andres Freund, Thomas Munro. Discussion: https://www.postgresql.org/message-id/CAGECzQSU2iGuocuP+fmu89hmBmR3tb-TNyYKjCcL2M_zTCkAFw@mail.gmail.com Backpatch-through: 18