The following function is defined in src/suite.lisp:
(defun list-all-suites ()
"Returns an unordered LIST of all suites."
(hash-table-values *suite*))
The problem with it is that variable *suite* is not used to store a hash table of all suites, but the current test suite object.
Fortunately, this function is not used anywhere at the moment, and the corresponding symbol is not even exported.
Perhaps, *toplevel-suites* was intented to be used?