+DEFUN ("test-completion", Ftest_completion, Stest_completion, 2, 3, 0,
+ doc: /* Return non-nil if STRING is a valid completion.
+Takes the same arguments as `all-completions' and `try-completion'.
+If ALIST is a function, it is called with three arguments:
+the values STRING, PREDICATE and `lambda'. */)
+ (string, alist, predicate)
+ Lisp_Object string, alist, predicate;