The easiest approach is to test a switch port with a directly connected laptop. If it links at full speed it's likely OK. Run a performance test with a known-good partner (e.g. using iperf3) to make sure.

If the port doesn't link at full speed, check its config and admin status (enabled/disabled). If all that looks fine but there's no link, the port is dead.

You might want to mark damaged port to avoid them in the future. You can use 8P8C dust caps or simply cut-off cable plugs. Also, you might want to use a different color for the ISDN patches.

If a port has been tested good but still performs poorly in real use your cabling is likely faulty. You can check the runs with the above method, even without the switch.

The easiest approach is to test a switch port with a directly connected laptop. If it links at full speed it's likely OK. Run a performance test with a known-good partner (e.g. using iperf3) to make sure.

If the port doesn't link at full speed, check its config and admin status (enabled/disabled). If all that looks fine but there's no link, the port is dead.

You might want to mark damaged port to avoid them in the future. You can use 8P8C dust caps or simply cut-off plugs from old patch cables. Also, you might want to use a different color for the ISDN patches.

If a port has been tested good but still performs poorly in real use your cabling is likely faulty. You can check the runs with the above method, even without the switch.