use crate::CharCounter; #[test]fn test_char_counter_sequential() {    let mut counter = CharCounter::new("It’s a 🌯!");    assert_eq!(counter.char_offset(0), Some(0.into())); // I    assert_eq!(counter.char_offset(1), Some(1.into())); // t    assert_eq!(counter.char_offset(2), Some(2.into())); // ’ (3 bytes)    assert_eq!(counter.char_offset(5), Some(3.into())); // s    assert_eq!(counter.char_offset(6), Some(4.into())); // <space>    assert_eq!(counter.char_offset(7), Some(5.into())); // a    assert_eq!(counter.char_offset(8), Some(6.into())); // <space>    assert_eq!(counter.char_offset(9), Some(7.into())); // 🌯 (4 bytes)    assert_eq!(counter.char_offset(13), Some(8.into())); // !} #[test]fn test_char_counter_out_of_order_fails() {    let mut counter = CharCounter::new("words");    assert_eq!(counter.char_offset(2), Some(2.into()));    // Because the iterator only advances forwards, using an earlier offset is unsupported.    assert_eq!(counter.char_offset(1), None);} #[test]fn test_char_counter_non_boundary() {    let mut counter = CharCounter::new("It’s a 🌯!");    // Byte 11 is in the middle of the emoji.    assert_eq!(counter.char_offset(11), None);} #[test]fn test_char_counter_out_of_bounds() {    let mut counter = CharCounter::new("short string");    assert_eq!(counter.char_offset(7), Some(7.into()));    assert_eq!(counter.char_offset(100), None);} #[test]fn test_char_counter_nonsequential() {    let mut counter = CharCounter::new("It’s a 🌯!");     // Skip ahead to the t.    assert_eq!(counter.char_offset(1), Some(1.into()));     // Now, skip past the multi-byte apostrophe to the first space.    assert_eq!(counter.char_offset(6), Some(4.into()));     // Skip ahead to the emoji.    assert_eq!(counter.char_offset(9), Some(7.into()));}