migrating partition to a 2015 MacBook Pro I'm a developer and through the years with my MacBook Pro early 2011 I installed and configured a lot of stuff to help me in my job.
I would like to buy a new MacBook pro but don't want to spend days/weeks installing everything again.
Since the Mac migration assistant won't copy everything, is there a way to duplicate the partition from my old mac to a new MacBook Pro (which can't be opened) ? 

edit:

by "can't be opened" I mean I can't take the hard drive and clone my current one with a third computer.

To my knownledge the migration assistant won't copy kernel modules for instance.
You can use Thunerbolt/FireWire to boot a Mac into Target-Mode to use it as a drive. Than you can clone it using disk utility, like you would clone a regular external drive. Next you'll (probably) need to reinstall OS X on the new MacBook Pro over that partition (so you have the latest OS X with all the drivers for the new device and whatnot), you can either do that by first creating a bootable USB (DiskMaker X is an easy solution for that) or by using Internet Recovery (boot the Mac while holding cmd+alt/option+R).