pub fn truncate(s: &str, max_len: usize) -> String {
if s.len() <= max_len {
s.to_string()
} else {
format!("{}...", &s[..max_len - 3])
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_truncate() {
assert_eq!(truncate("short", 10), "short");
assert_eq!(truncate("a very long string", 10), "a very ..."); }
}