There is really only one way to verify that the RAID1 is functional and that is to pull a drive and see if the data remains available.
It should be noted that your "proposed test" would require a successful rebuild or resync - whilst automatic rebuilds or resyncs are desirable they are not essential, and the only thing that would have to be present for RAID1 to be deemed functional is the ability of the system to remain online and functional after the failure of a hard disk.
A quick visual check can be done by observing the drive activity LEDs whilst writing to the disk (a read can be done from either disk) - both should flash, but I hasten to point out that this is not always apparent when copying or transferring small quantities of data, and you can also pull the disks and connect them to any system capable of reading an ext2 file system and verifying that your data is present - if this is done without powering the unit up without the disks, there should be no problem resulting from it.
