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Your Mac OS X was probably using EFI GPT partition table and grub may be detecting it.

When you start TestDisk, select the disk and choose EFI GPT, Analyse.
If you see your partitions, take a screenshot, save this screenshot somewhere safe, select Backup, choose Quick Search, Load the backup, use your screenshot to get the same partitions, go on next screen, compare with the screenshot and if the results are ok, choose to rewrite the partition table.

You will have to repair your installation to repair the damage caused by dd, but if no mistake is done, you should be able to boot again and access all your data.

TestDisk can't list the content of HFS partition. Usually for the correct HFS partition, TestDisk 7.0 or later will display at the bottom of the screen some information (ie. blocksize) and " + Backup".

As the beginning of the partition may have been overwritten, fsck may have to use a backup HFS block to access and repair the filesystem.