pub fn prompt<R>(prompt_text: &str, mut reader: R) -> String

where

    R: BufRead,

    print!("{}", prompt_text);

    io::stdout().flush().expect("Failed to flush stdout.");

    let mut input = String::new();

    reader.read_line(&mut input).expect("Failed to read input.");

    input.trim().to_lowercase()

}

    fn test_prompt() {

        let prompt_text = "Enter some text: ";

        let expected = "hello";

        let reader = std::io::Cursor::new(format!("{}\n", expected));

        let actual = prompt(prompt_text, reader);

        assert_eq!(actual, expected);

    }