improve error message

src/parser/parser_test.ts

@@ -198,7 +198,7 @@ Deno.test("AST all distinct", () => {
     const ast = parse(sentence).unwrap();
     for (const [i, a] of ast.entries()) {
       for (const b of ast.slice(i + 1)) {
-        assertNotEquals(a, b);
+        assertNotEquals(a, b, `Error at ${sentence}`);
       }
     }
   }