$ cargo r
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.01s
     Running `target/debug/rontest`

thread 'main' (741474) panicked at src/main.rs:2:3:
assertion `left == right` failed
  left: Err(SpannedError { code: TrailingCharacters, span: Span { start: Position { line: 1, col: 4 }, end: Position { line: 1, col: 4 } } })
 right: Ok(10)
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace