The guide below explains how to install OS X Yosemite 10.10 in a virtual machine using the free and powerful VirtualBox.

It's based on this pastebin I've found via Google, markdownified and adjusted to work with the official Yosemite release.

Legal disclaimer: This guide aims to explain how to create a virtual machine on a regularly purchased Apple computer, running a genuine Mac OS X operating system, for testing purposes only.

Howto

1. Download Yosemite from the App Store
2. Open Terminal.app
3. Install iesd, to customize OS X InstallESD:
   gem install iesd
4. Turn install image into base system:
   iesd -i "/Applications/Install OS X Yosemite.app" -o yosemite.dmg -t BaseSystem
5. Convert into UDSP (sparse image) format:
   hdiutil convert yosemite.dmg -format UDSP -o yosemite.sparseimage
6. Mount the InstallESD ...
   hdiutil mount "/Applications/Install OS X Yosemite.app/Contents/SharedSupport/InstallESD.dmg"
7. ... as well as the sparse image:
   hdiutil mount yosemite.sparseimage
8. Copy base system into sparse image:
   cp "/Volumes/OS X Install ESD/BaseSystem."* "/Volumes/OS X Base System/"
9. Unmound InstallESD ...
   hdiutil unmount "/Volumes/OS X Install ESD/"
10. ... as well as the sparse image:
    hdiutil unmount "/Volumes/OS X Base System/"
11. Unmount both mounted disks:
    
    • via diskutil:
      diskutil unmountDisk $(diskutil list | grep "OS X Base System" -B 4 | head -1)
diskutil unmountDisk $(diskutil list | grep "OS X Install ESD" -B 4 | head -1)
    • if that doesn't work and you get a "resource busy" message in step 12, try using the Disk Utility:
      
12. Convert back to UDZO format (compressed image):
    hdiutil convert yosemite.sparseimage -format UDZO -o yosemitefixed.dmg
13. Add yosemitefixed.dmg as a live cd in virtual box
14. Change the chipset of your virtual machine to "PIIX3"
15. Start your VM, open Disk Utility within installer and create a new HFS+ partition on the virtual disk
16. Install it!

FAQ

Error message: "Kernel driver not installed (rc=-1908)"

Try to reinstall VirtualBox to fix this error

Stuck on boot: "Missing Bluetooth Controller Transport"

Try the following steps to fix this issue:

1. Stop the virtual machine in VirtualBox
2. Open a new terminal window
3. Run the following command to adjust the guest CPU (Replace <YourVMname> with your actual VM name):
   VBoxManage modifyvm '<YourVMname>' --cpuidset 1 000206a7 02100800 1fbae3bf bfebfbff

Sources

• http://www.engadget.com/discuss/how-to-install-os-x-yosemite-inside-virtualbox-1rey/
• http://forums.macrumors.com/showthread.php?p=19191255
• http://pastebin.com/rFmQvFWc