Howto create a package that contains the build dependencies of the package you want to test:

Using equivs

1. Download the source package of the package you want to test:
   $ apt-get source [packagename]
2. Create a dummy package:
   $ equivs-control [packagename]-builddep
3. In the file [packagename]-builddep do the following:
   1. Set the field Package to [packagename]-builddep
   2. Set the field Version to the version of the package
   3. Copy the Build-Depends lines from debian/control to the Depends section
   4. Change the word Build-Depends to Depends
4. Build the *.deb file:
   $ equivs-build [packagename]-builddep
5. Add the package to the list of known packages:
   $ sudo dpkg -i *.deb
6. Install the dependencies:
   $ sudo aptitude install [packagename]-builddep

Using devscripts

Alternative: mk-build-deps and then continue from step 5.