I have recently started using tape backups for long term recovery, is there anyway I can test the restores from tape without overwriting existing data?
What type of the tape job you're using? Backup to tape or File to tape one?
Files backed up by backup to tape job, can be restored either to any repository (Backup repository) you have or to whatever location you want to (This server; Folder path).
As to files backed up by files to tape job, there are two restore options - "original location" and "this server".
Either way, you should use "This server" option in order to restore files to different location, so that, current files aren't overwritten.
Is there also a way to see what data is on the tape?
In case of backup to tape job, there is a predefined report in Veeam ONE called “Tape Backups” that lists VM restore points along with the tapes they reside on; might be exactly what you're looking for.
Otherwise (file to tape job), go to "Files" node, select required files -> properties -> restore points, and see tapes given file/directory resides on.