Add a test for Usexp.Atom.is_valid

test/unit-tests/jbuild

@@ -9,6 +9,15 @@
 
 (ocamllex (expect_test))
 
+(executable
+ ((name sexp_tests)
+  (modules (sexp_tests))
+  (libraries (stdune usexp))))
+
+(alias
+ ((name runtest)
+  (action (run ./sexp_tests.exe))))
+
 (alias
  ((name runtest)
   (deps (tests.mlt

test/unit-tests/sexp_tests.ml

@@ -0,0 +1,30 @@
+open! Stdune
+
+let () = Printexc.record_backtrace true
+
+(* Test that all strings of length <= 3 such that [Usexp.Atom.is_valid
+   s] are recignized as atoms by the parser *)
+let () =
+  for len = 0 to 3 do
+    let s = Bytes.create len in
+    for i = 0 to 1 lsl (len * 8) - 1 do
+      if len > 0 then Bytes.set s 0 (Char.chr ( i        land 0xff));
+      if len > 1 then Bytes.set s 1 (Char.chr ((i lsr 4) land 0xff));
+      if len > 2 then Bytes.set s 2 (Char.chr ((i lsr 8) land 0xff));
+      let s = Bytes.unsafe_to_string s in
+      let parser_recognizes_as_atom =
+        match Usexp.parse_string ~fname:"" ~mode:Single s with
+        | exception _    -> false
+        | Atom (_, A s') -> s = s'
+        | _              -> false
+      in
+      if Usexp.Atom.is_valid s && not parser_recognizes_as_atom then begin
+        Printf.eprintf
+          "Usexp.Atom.is_valid error:\n\
+           - s = %S\n\
+           - Usexp.Atom.is_Valid s = %B\n"
+          s (Usexp.Atom.is_valid s);
+        exit 1
+      end
+    done
+  done