use std::fs;
fn open_file(file_path: &str) -> String {
    fs::read_to_string(file_path).expect("Failed to read file")
}
fn main() {
    let contents = open_file("test.txt");
    println!("{}", contents);
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_open_file() {
        let content: String = open_file("test.txt");
        assert_eq!(content, "hello world\n");
    }
}