io::Write,

// A custom type for log output. We need this to hide log messages

// from output in successful tests. Cargo will hide standard output

// and error by default, which is what we want, but it seems this only

// applies to output via the `print!` family of macros. If we open a

// new handle for stdout or stderr, output via that handle is not

// captured by Cargo.

//

// Instead, we have our own log writer type that writes to stderr in

// production mode, and uses `print!` in tests.

#[derive(Default)]

struct LogWriter {}

#[cfg(test)]

impl Write for LogWriter {

    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {

        let s = String::from_utf8_lossy(buf);

        print!("{s}");

        Ok(buf.len())

    }

    fn flush(&mut self) -> std::io::Result<()> {

        Ok(())

    }

}

#[cfg(not(test))]

impl Write for LogWriter {

    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {

        let mut stderr = std::io::stderr();

        stderr.write_all(buf)?;

        stderr.flush()?;

        Ok(buf.len())

    }

    fn flush(&mut self) -> std::io::Result<()> {

        Ok(())

    }

}

    let underlying_logger = slog_json::Json::new(LogWriter::default())