Remove comments about bugs in DataTracker

These were relevant during development as TODOs, but have since
been resolved, but the tests were not updated.

Added sufficient assertions to validate that the code behaves
as expected regarding merging additional TSN blocks.

Author: boivie

src/rx/data_tracker.rs

@@ -1248,9 +1248,9 @@ mod tests {
         // Create two separate blocks: 12-13 and 15-16
         observe(&mut d, now, &[12, 13, 15, 16]);
         // Now fill the gap between them with 14. This should merge the blocks.
-        // The current implementation of `add_additional_tsn` is buggy and will
-        // result in `[12..14, 14..17]`.
         observe(&mut d, now, &[14]);
+        assert_eq!(d.additional_tsn_blocks, vec![Tsn(12)..Tsn(17)]);
+
         // Now receive 11, which should advance the cumulative ack over all blocks.
         observe(&mut d, now, &[11]);
 
@@ -1268,21 +1268,20 @@ mod tests {
         // Create two separate blocks: 13 and 15.
         // State: additional_tsn_blocks = [13..14, 15..16]
         observe(&mut d, now, &[13, 15]);
+        assert_eq!(d.additional_tsn_blocks, vec![Tsn(13)..Tsn(14), Tsn(15)..Tsn(16)]);
 
         // Fill the gap between them with 14.
-        // This hits a bug in `add_additional_tsn` where expanding a block to the left
-        // doesn't check if it can merge with the block before it, resulting in adjacent blocks.
-        // State: additional_tsn_blocks = [13..14, 14..16]
         observe(&mut d, now, &[14]);
+        assert_eq!(d.additional_tsn_blocks, vec![Tsn(13)..Tsn(16)]);
 
         // Add 12, which expands the first block to the left.
-        // State: additional_tsn_blocks = [12..14, 14..16]
         observe(&mut d, now, &[12]);
+        assert_eq!(d.additional_tsn_blocks, vec![Tsn(12)..Tsn(16)]);
 
         // Now receive 11, which should advance the cumulative ack over all blocks.
-        // But `observe` only processes one block, leaving last_cumulative_acked_tsn
-        // at 13 instead of 15.
         observe(&mut d, now, &[11]);
+        assert_eq!(d.last_cumulative_acked_tsn, Tsn(15));
+        assert_eq!(d.additional_tsn_blocks, vec![]);
 
         let sack = d.create_selective_ack(A_RWND);
         assert_eq!(sack.cumulative_tsn_ack, Tsn(15));