[RUST] How to test println?

how-to-test-println.rs

// ❌ not testable
fn greeting_hard_to_test(nb: i32, name: &str) {
    for _ in 0..nb {
        println!("hi {}", name);
    }
}

// ✅ easy to test
trait Logger {
    fn log(&mut self, value: String);
}
struct ConsoleLogger;

impl Logger for ConsoleLogger {
    fn log(&mut self, value: String) {
        println!("{}", value);
    }
}
fn greeting(nb: i32, name: &str, logger: &mut dyn Logger) {
    for _ in 0..nb {
        logger.log(format!("hi {}", name));
    }
}

#[cfg(test)]
mod tests { 
    use super::*;  
    #[derive(Default)]
    struct TestLogger(Vec<String>);
    impl Logger for TestLogger {
        fn log(&mut self, value: String) {
            self.0.push(value);
        }
    }
    #[test]
    fn greeting_test() {
        let mut test_logger = TestLogger::default();
        greeting(2, "maxday", &mut test_logger);
        assert_eq!(2, test_logger.0.len());
        assert_eq!("hi maxday", test_logger.0[0]);
        assert_eq!("hi maxday", test_logger.0[1]);
    }
}