interactive function name

[Ritchie]

I'm trying to use the interactive function name feature. On emacs lisp
manual it says:

‘a’
A function name (i.e., a symbol satisfying fboundp). Existing,
Completion, Prompt.

So I tried it with a small test code:

(defun testfun1 ()
  (message "hello, world!"))

(defun test (abcd)
  (interactive "aTheme name: ")
  (abcd))

Emacs gives an error saying,

test: Symbol's function definition is void: abcd

I tried to test abcd with fboundp, it returns t. So I'm quite confused
about how to use the 'a' option in interactive.
Any body can give some hints?