smartctl -t long /dev/sdc
smartctl 7.1 2019-12-30 r5022 [x86_64-linux-5.7.0-gentoo] (local build)
Copyright (C) 2002-19, Bruce Allen, Christian Franke, www.smartmontools.org

=== START OF OFFLINE IMMEDIATE AND SELF-TEST SECTION ===
Sending command: "Execute SMART Extended self-test routine immediately in off-line mode".
Drive command "Execute SMART Extended self-test routine immediately in off-line mode" successful.
Testing has begun.
Please wait 402 minutes for test to complete.
Test will complete after Sun Jun  7 04:07:14 2020 BST
Use smartctl -X to abort test.