message: Use '' for char instead of ""
diff: @@ -79,7 +79,7 @@ impl DocTestBinaryMeta {
  if let Some(Component::Normal(folder)) = test.as_ref().components().nth_back(1) {
  let temp = folder.to_string_lossy();
  let file_end = temp.rfind("rs").map(|i| i + 2)?;
  - let end = temp.rfind("_")?;
  + let end = temp.rfind('_')?;
  if end > file_end + 1 {
  let line = temp[(file_end + 1)..end].parse::<usize>().ok()?;
  Some(Self {
  