(define-condition test-condition (error)
  ((test-slot :reader test-slot :initarg :test-slot)))

(defun test-function ()
  (restart-case
      (error 'test-condition :test-slot 1)
    (testable-restart ()
      :report "Visible restart."
      :test (lambda (c) (format t ";; From restart test function: ~A~%" c)
              (and (typep c 'test-condition) (eql (test-slot c) 1)))
      nil)))

* (test-function)
;; From restart test function: Condition COMMON-LISP-USER::TEST-CONDITION was signalled.

debugger invoked on a TEST-CONDITION in thread
#<THREAD "main thread" RUNNING {10008A8083}>:
  Condition COMMON-LISP-USER::TEST-CONDITION was signalled.

Type HELP for debugger help, or (SB-EXT:EXIT) to exit from SBCL.

restarts (invokable by number or by possibly-abbreviated name):
  0: [TESTABLE-RESTART] Visible restart.
  1: [ABORT           ] Exit debugger, returning to top level.

(TEST-FUNCTION)
   source: (RESTART-CASE (ERROR 'TEST-CONDITION :TEST-SLOT 1)
             (TESTABLE-RESTART NIL :REPORT "Visible restart." :TEST
              (LAMBDA (C)
                (FORMAT T ";; From restart test function: ~A~%" C)
                (AND (TYPEP C 'TEST-CONDITION) (EQL (TEST-SLOT C) 1)))
;; From restart test function: NIL
              NIL))