Copy file in home directory during Homebrew formula install

Is it possible to create files outside of /usr/local/Cellar during a Homebrew formula installation? Here is my code:

def install           
    cmd = "whoami; cd /Users/hughcrt; pwd; mkdir test"
    value = #{cmd}
    print value
end

And when I do brew install --build-from-source my-formula I get:

mkdir: test: Operation not permitted
hughcrt
/Users/hughcrt

It don't understand why I can't create a file as the user in the script is hughcrt and I'm in the right directory