git checkout master
git pull
git checkout mybranch
git merge master
# to keep mybranch in sync with master
# then when you're ready to put mobiledevicesupport into master, first merge in master like above, then ...
git checkout master
git merge mybranch
git push origin master
git checkout test-branch //Checkout the branch you want to update
git merge master //Merge all code from master to test-branch
// When your are done with test-branch you can merge all code into master branch
git checkout master // Make sure you are on master branch
git merge test-branch