Improve tests for lint 'mutability_check'

Signed-off-by: Kakadu <[email protected]>

tests/typed/hashtables.t/.zanuda

@@ -0,0 +1 @@
+forward mutability_check ignore tast.ml,tast.ml,tast.ml,tast.ml

tests/typed/hashtables.t/Counter.ml

@@ -0,0 +1,3 @@
+let count =
+  let last = ref 0 in
+  (fun () -> incr last; !last)

tests/typed/hashtables.t/dune

@@ -2,4 +2,4 @@
  (name test_hashtables)
  (wrapped false)
  (libraries base)
- (modules Hashtables))
+ (modules Hashtables Counter Tast))

tests/typed/hashtables.t/run.t

@@ -32,3 +32,11 @@
   24 | type args = { mutable count: int }
                      ^^^^^^^^^^^^^^^^^^
   Alert zanuda-linter: Using mutable data structures for teaching purposes is usually discouraged. Replace Hashtables by standard tree-like maps or consider Hash-Array Mapped Tries (HAMT). Use mutable `ref`erences and mutable structure fields only if it is really required. In all places where it is needed indeed, describe in a comment why it is needed there.
+  File "Counter.ml", line 3, characters 18-22:
+  3 |   (fun () -> incr last; !last)
+                        ^^^^
+  Alert zanuda-linter: Using mutable data structures for teaching purposes is usually discouraged. Replace Hashtables by standard tree-like maps or consider Hash-Array Mapped Tries (HAMT). Use mutable `ref`erences and mutable structure fields only if it is really required. In all places where it is needed indeed, describe in a comment why it is needed there.
+  File "Counter.ml", line 3, characters 25-29:
+  3 |   (fun () -> incr last; !last)
+                               ^^^^
+  Alert zanuda-linter: Using mutable data structures for teaching purposes is usually discouraged. Replace Hashtables by standard tree-like maps or consider Hash-Array Mapped Tries (HAMT). Use mutable `ref`erences and mutable structure fields only if it is really required. In all places where it is needed indeed, describe in a comment why it is needed there.

tests/typed/hashtables.t/tast.ml

@@ -0,0 +1,3 @@
+(** Report about this line will not appear because of .zanuda file  *)
+let last = ref 0
+let() = incr last