more doc and test for CCRandom

src/core/CCRandom.ml

@@ -118,6 +118,13 @@ let split_list i ~len st =
   else
     None
 
+(*$Q
+  Q.(pair small_int small_int) (fun (i,j) -> \
+    let len, n = min i j, max i j in \
+    let l = QCheck.Gen.generate1 (split_list n ~len) in \
+    match l with None -> true | Some l -> l<> [] && List.for_all (fun x->x>0) l)
+*)
+
 let retry ?(max=10) g st =
   let rec aux n =
     match g st with

src/core/CCRandom.mli

@@ -102,7 +102,8 @@ val split : int -> (int * int) option t
 
 val split_list : int -> len:int -> int list option t
 (** Split a value [n] into a list of values whose sum is [n]
-    and whose length is [length].
+    and whose length is [length]. The list is never empty and does not
+    contain [0].
     @return [None] if the value is too small *)
 
 val retry : ?max:int -> 'a option t -> 'a option t