test: add non-empty coverage for TxUpdate

crates/core/tests/test_tx_update.rs

@@ -1,9 +1,61 @@
 use bdk_core::TxUpdate;
 
+use bitcoin::{absolute::LockTime, transaction::Version, Transaction, Txid};
+use bitcoin::hashes::Hash;
+use std::sync::Arc;
+
 #[test]
 fn test_empty() {
     assert!(
         TxUpdate::<()>::default().is_empty(),
         "Default `TxUpdate` must be empty"
     );
 }
+
+#[test]
+fn test_not_empty_when_txs_present() {
+    let mut u = TxUpdate::<()>::default();
+
+    let tx = Arc::new(Transaction {
+        version: Version::ONE,
+        lock_time: LockTime::ZERO,
+        input: vec![],
+        output: vec![],
+    });
+
+    u.txs.push(tx);
+
+    assert!(
+        !u.is_empty(),
+        "`TxUpdate` must not be empty when `txs` is populated"
+    );
+}
+
+#[test]
+fn test_not_empty_when_seen_ats_present() {
+    let mut u = TxUpdate::<()>::default();
+
+    let txid = Txid::from_byte_array([1u8; 32]);
+    u.seen_ats.insert((txid, 123));
+
+    assert!(
+        !u.is_empty(),
+        "`TxUpdate` must not be empty when `seen_ats` is populated"
+    );
+}
+
+#[test]
+fn test_extend_makes_update_non_empty() {
+    let mut a = TxUpdate::<()>::default();
+    let mut b = TxUpdate::<()>::default();
+
+    let txid = Txid::from_byte_array([2u8; 32]);
+    b.seen_ats.insert((txid, 999));
+
+    a.extend(b);
+
+    assert!(
+        !a.is_empty(),
+        "`TxUpdate` must not be empty after extending with a non-empty update"
+    );
+}