add some test

test/utf8.ml

@@ -0,0 +1,19 @@
+open Printf
+
+let next_tok buf =
+  let open Sedlexing.Utf8 in
+  match%sedlex buf with
+    | "a", Utf8 (Chars "+-×÷") -> sprintf "with Chars: %s" (lexeme buf)
+    | "b", Utf8 ("+" | "-" | "×" | "÷") ->
+        sprintf "with or_pattern: %s" (lexeme buf)
+    | _ -> failwith (sprintf "Unexpected character: %s" (lexeme buf))
+
+let%expect_test _ =
+  Sedlexing.Utf8.from_string "a+" |> next_tok |> print_string;
+  [%expect {| with Chars: a+ |}];
+  Sedlexing.Utf8.from_string "a÷" |> next_tok |> print_string;
+  [%expect {| with Chars: a÷ |}];
+  Sedlexing.Utf8.from_string "b+" |> next_tok |> print_string;
+  [%expect {| with or_pattern: b+ |}];
+  Sedlexing.Utf8.from_string "b÷" |> next_tok |> print_string;
+  [%expect {| with or_pattern: b÷ |}]