First somewhat working version attached...

It finds 1387 tests in 328 suites.

The original finds 2611 tests in 349 suites.

That's because skip-comments is somehow broken.

An example where it has an error very early is tests/core/futils.c :

(use-modules (ice-9 ftw))
(use-modules (ice-9 regex))
(use-modules (ice-9 getopt-long))
(use-modules (ice-9 rdelim))
(use-modules (ice-9 match))
(use-modules (ice-9 textual-ports))
(use-modules (srfi srfi-1))

(define fname "test/core/futils.c")
(define s (call-with-input-file fname get-string-all))

(define (replace needle replacement haystack)
  "Replace all occurences of NEEDLE in HAYSTACK by REPLACEMENT.
NEEDLE is a regular expression."
  (regexp-substitute/global #f needle haystack 'pre replacement 'post))

(define (skip-comments text)
  (replace (string-append "//[^\n]*?|"
                          "/[*].*?[*]/|"
                          "'([.]|[^'])*?'|"
                          "\"([.]|[^\"])*?\"")
           "" text))

(write (skip-comments s)) ; very short, for some reason