What's the difference between SMART "long" and "offline" tests?

What's the difference between the two below? What exactly is tested by each test?

smartctl -t offline /dev/sda
smartctl -t long /dev/sda

According to the [smartctl](https://manpages.ubuntu.com/manpages/noble/en/man8/smartctl.8.html) documentation: > *offline* - [ATA] runs SMART Immediate Offline Test. This immediately starts the test described above. This command can be given during normal system operation. The effects of this test are visible only in that it updates the SMART Attribute values, and if errors are found they will appear in the SMART error log, visible with the '-l error' option. > > *offline* - [SCSI] runs the default self test in foreground. No entry is placed in the self test log. > > *long* - [ATA] runs SMART Extended Self Test (tens of minutes to several hours). This is a longer and more thorough version of the Short Self Test described above. Note that this command can be given during normal system operation (unless run in captive mode - see the '-C' option below). > > *long* - [SCSI] runs the "Background long" self-test. However, this description is somewhat vague and I still don't fully understand the actual difference. Also, which of the tests performs a complete surface scan and sector reallocation if needed?