test: add non-empty coverage for SyncResponse and FullScanResponse

crates/core/tests/test_spk_client.rs

@@ -1,5 +1,9 @@
+use bdk_chain::local_chain::CheckPoint;
 use bdk_core::spk_client::{FullScanResponse, SyncResponse};
 
+use bitcoin::hashes::Hash;
+use bitcoin::BlockHash;
+
 #[test]
 fn test_empty() {
     assert!(
@@ -11,3 +15,27 @@ fn test_empty() {
         "Default `SyncResponse` must be empty"
     );
 }
+
+#[test]
+fn test_sync_response_not_empty_when_chain_update_present() {
+    let mut resp = SyncResponse::<()>::default();
+
+    let bh = BlockHash::from_byte_array([0u8; 32]);
+    resp.chain_update = Some(CheckPoint::new(0, bh));
+
+    assert!(
+        !resp.is_empty(),
+        "SyncResponse must not be empty when chain_update is present"
+    );
+}
+
+#[test]
+fn test_full_scan_response_not_empty_when_last_active_indices_present() {
+    let mut resp = FullScanResponse::<(), ()>::default();
+    resp.last_active_indices.insert((), 0);
+
+    assert!(
+        !resp.is_empty(),
+        "FullScanResponse must not be empty when last_active_indices is present"
+    );
+}