diff --git a/crates/transaction-pool/src/identifier.rs b/crates/transaction-pool/src/identifier.rs
index 876fa00dca..37a3450e06 100644
--- a/crates/transaction-pool/src/identifier.rs
+++ b/crates/transaction-pool/src/identifier.rs
@@ -5,15 +5,15 @@ use std::collections::HashMap;
 
 /// An internal mapping of addresses.
 ///
-/// This assigns a _unique_ `SenderId` for a new `Address`.
+/// This assigns a _unique_ [`SenderId`] for a new [`Address`].
 /// It has capacity for 2^64 unique addresses.
 #[derive(Debug, Default)]
 pub struct SenderIdentifiers {
     /// The identifier to use next.
     id: u64,
-    /// Assigned `SenderId` for an `Address`.
+    /// Assigned [`SenderId`] for an [`Address`].
     address_to_id: HashMap<Address, SenderId>,
-    /// Reverse mapping of `SenderId` to `Address`.
+    /// Reverse mapping of [`SenderId`] to [`Address`].
     sender_to_address: FxHashMap<SenderId, Address>,
 }
 
@@ -24,12 +24,12 @@ impl SenderIdentifiers {
         self.sender_to_address.get(id)
     }
 
-    /// Returns the `SenderId` that belongs to the given address, if it exists
+    /// Returns the [`SenderId`] that belongs to the given address, if it exists
     pub fn sender_id(&self, addr: &Address) -> Option<SenderId> {
         self.address_to_id.get(addr).copied()
     }
 
-    /// Returns the existing `SendId` or assigns a new one if it's missing
+    /// Returns the existing [`SenderId`] or assigns a new one if it's missing
     pub fn sender_id_or_create(&mut self, addr: Address) -> SenderId {
         self.sender_id(&addr).unwrap_or_else(|| {
             let id = self.next_id();
@@ -39,11 +39,11 @@ impl SenderIdentifiers {
         })
     }
 
-    /// Returns a new address
+    /// Returns the current identifier and increments the counter.
     fn next_id(&mut self) -> SenderId {
         let id = self.id;
         self.id = self.id.wrapping_add(1);
-        SenderId(id)
+        id.into()
     }
 }
 
@@ -54,10 +54,8 @@ impl SenderIdentifiers {
 #[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
 pub struct SenderId(u64);
 
-// === impl SenderId ===
-
 impl SenderId {
-    /// Returns a `Bound` for `TransactionId` starting with nonce `0`
+    /// Returns a `Bound` for [`TransactionId`] starting with nonce `0`
     pub const fn start_bound(self) -> std::ops::Bound<TransactionId> {
         std::ops::Bound::Included(TransactionId::new(self, 0))
     }
@@ -81,34 +79,29 @@ pub struct TransactionId {
     pub nonce: u64,
 }
 
-// === impl TransactionId ===
-
 impl TransactionId {
     /// Create a new identifier pair
     pub const fn new(sender: SenderId, nonce: u64) -> Self {
         Self { sender, nonce }
     }
 
-    /// Returns the `TransactionId` this transaction depends on.
+    /// Returns the [`TransactionId`] this transaction depends on.
     ///
     /// This returns `transaction_nonce - 1` if `transaction_nonce` is higher than the
     /// `on_chain_nonce`
     pub fn ancestor(transaction_nonce: u64, on_chain_nonce: u64, sender: SenderId) -> Option<Self> {
-        if transaction_nonce == on_chain_nonce {
-            return None
-        }
-        let prev_nonce = transaction_nonce.saturating_sub(1);
-        (on_chain_nonce <= prev_nonce).then(|| Self::new(sender, prev_nonce))
+        (transaction_nonce > on_chain_nonce)
+            .then(|| Self::new(sender, transaction_nonce.saturating_sub(1)))
     }
 
-    /// Returns the `TransactionId` that would come before this transaction.
+    /// Returns the [`TransactionId`] that would come before this transaction.
     pub fn unchecked_ancestor(&self) -> Option<Self> {
         (self.nonce != 0).then(|| Self::new(self.sender, self.nonce - 1))
     }
 
-    /// Returns the `TransactionId` that directly follows this transaction: `self.nonce + 1`
+    /// Returns the [`TransactionId`] that directly follows this transaction: `self.nonce + 1`
     pub const fn descendant(&self) -> Self {
-        Self::new(self.sender, self.nonce + 1)
+        Self::new(self.sender, self.next_nonce())
     }
 
     /// Returns the nonce that follows immediately after this one.
@@ -123,6 +116,67 @@ mod tests {
     use super::*;
     use std::collections::BTreeSet;
 
+    #[test]
+    fn test_transaction_id_new() {
+        let sender = SenderId(1);
+        let tx_id = TransactionId::new(sender, 5);
+        assert_eq!(tx_id.sender, sender);
+        assert_eq!(tx_id.nonce, 5);
+    }
+
+    #[test]
+    fn test_transaction_id_ancestor() {
+        let sender = SenderId(1);
+
+        // Special case with nonce 0 and higher on-chain nonce
+        let tx_id = TransactionId::ancestor(0, 1, sender);
+        assert_eq!(tx_id, None);
+
+        // Special case with nonce 0 and same on-chain nonce
+        let tx_id = TransactionId::ancestor(0, 0, sender);
+        assert_eq!(tx_id, None);
+
+        // Ancestor is the previous nonce if the transaction nonce is higher than the on-chain nonce
+        let tx_id = TransactionId::ancestor(5, 0, sender);
+        assert_eq!(tx_id, Some(TransactionId::new(sender, 4)));
+
+        // No ancestor if the transaction nonce is the same as the on-chain nonce
+        let tx_id = TransactionId::ancestor(5, 5, sender);
+        assert_eq!(tx_id, None);
+
+        // No ancestor if the transaction nonce is lower than the on-chain nonce
+        let tx_id = TransactionId::ancestor(5, 15, sender);
+        assert_eq!(tx_id, None);
+    }
+
+    #[test]
+    fn test_transaction_id_unchecked_ancestor() {
+        let sender = SenderId(1);
+
+        // Ancestor is the previous nonce if transaction nonce is higher than 0
+        let tx_id = TransactionId::new(sender, 5);
+        assert_eq!(tx_id.unchecked_ancestor(), Some(TransactionId::new(sender, 4)));
+
+        // No ancestor if transaction nonce is 0
+        let tx_id = TransactionId::new(sender, 0);
+        assert_eq!(tx_id.unchecked_ancestor(), None);
+    }
+
+    #[test]
+    fn test_transaction_id_descendant() {
+        let sender = SenderId(1);
+        let tx_id = TransactionId::new(sender, 5);
+        let descendant = tx_id.descendant();
+        assert_eq!(descendant, TransactionId::new(sender, 6));
+    }
+
+    #[test]
+    fn test_transaction_id_next_nonce() {
+        let sender = SenderId(1);
+        let tx_id = TransactionId::new(sender, 5);
+        assert_eq!(tx_id.next_nonce(), 6);
+    }
+
     #[test]
     fn test_transaction_id_ord_eq_sender() {
         let tx1 = TransactionId::new(100u64.into(), 0u64);
@@ -140,4 +194,67 @@ mod tests {
         let set = BTreeSet::from([tx1, tx2]);
         assert_eq!(set.into_iter().collect::<Vec<_>>(), vec![tx1, tx2]);
     }
+
+    #[test]
+    fn test_address_retrieval() {
+        let mut identifiers = SenderIdentifiers::default();
+        let address = Address::new([1; 20]);
+        let id = identifiers.sender_id_or_create(address);
+        assert_eq!(identifiers.address(&id), Some(&address));
+    }
+
+    #[test]
+    fn test_sender_id_retrieval() {
+        let mut identifiers = SenderIdentifiers::default();
+        let address = Address::new([1; 20]);
+        let id = identifiers.sender_id_or_create(address);
+        assert_eq!(identifiers.sender_id(&address), Some(id));
+    }
+
+    #[test]
+    fn test_sender_id_or_create_existing() {
+        let mut identifiers = SenderIdentifiers::default();
+        let address = Address::new([1; 20]);
+        let id1 = identifiers.sender_id_or_create(address);
+        let id2 = identifiers.sender_id_or_create(address);
+        assert_eq!(id1, id2);
+    }
+
+    #[test]
+    fn test_sender_id_or_create_new() {
+        let mut identifiers = SenderIdentifiers::default();
+        let address1 = Address::new([1; 20]);
+        let address2 = Address::new([2; 20]);
+        let id1 = identifiers.sender_id_or_create(address1);
+        let id2 = identifiers.sender_id_or_create(address2);
+        assert_ne!(id1, id2);
+    }
+
+    #[test]
+    fn test_next_id_wrapping() {
+        let mut identifiers = SenderIdentifiers { id: u64::MAX, ..Default::default() };
+
+        // The current ID is `u64::MAX`, the next ID should wrap around to 0.
+        let id1 = identifiers.next_id();
+        assert_eq!(id1, SenderId(u64::MAX));
+
+        // The next ID should now be 0 because of wrapping.
+        let id2 = identifiers.next_id();
+        assert_eq!(id2, SenderId(0));
+
+        // And then 1, continuing incrementing.
+        let id3 = identifiers.next_id();
+        assert_eq!(id3, SenderId(1));
+    }
+
+    #[test]
+    fn test_sender_id_start_bound() {
+        let sender = SenderId(1);
+        let start_bound = sender.start_bound();
+        if let std::ops::Bound::Included(tx_id) = start_bound {
+            assert_eq!(tx_id, TransactionId::new(sender, 0));
+        } else {
+            panic!("Expected included bound");
+        }
+    }
 }
diff --git a/crates/transaction-pool/src/pool/mod.rs b/crates/transaction-pool/src/pool/mod.rs
index a00d6522d1..1878242eee 100644
--- a/crates/transaction-pool/src/pool/mod.rs
+++ b/crates/transaction-pool/src/pool/mod.rs
@@ -194,7 +194,7 @@ where
         self.pool.write().set_block_info(info)
     }
 
-    /// Returns the internal `SenderId` for this address
+    /// Returns the internal [`SenderId`] for this address
     pub(crate) fn get_sender_id(&self, addr: Address) -> SenderId {
         self.identifiers.write().sender_id_or_create(addr)
     }