It seems like several tests are failing because neither the seek nor the read return an error when seeking/reading beyond the end of the file. The Seek and Read traits seem to allow operations beyond EOF...read in particular will simply return 0 rather than produce an error. Perhaps read_range should not test the number of bytes returned at all and return what it can, leaving it up to the caller to detect when a read returns fewer bytes than requested and act accordingly. 🤷

Edit:
Ok, I read the discord discussion, so ignore the above. Instead, how about getting the actual file length from the File metadata, and then test that range.start is not beyond that?

    let file_len = metadata.len();
    ensure!(
        file_len > range.start as u64,
        OutOfRangeSnafu {
            path,
            expected: range.start,
            actual: file_len as usize
        }
    );

    let to_read = range.end - range.start;
    let seek_idx = file
        .seek(SeekFrom::Start(range.start as u64))
        .context(SeekSnafu { path })?;