Add validation

cpp/include/gar/graph.h

@@ -502,9 +502,7 @@ class EdgeIter {
   }
 
   /** Check if the current position is the end. */
-  bool is_end() const {
-    return global_chunk_index_ == chunk_end_ && cur_offset_ == 0;
-  }
+  bool is_end() const { return global_chunk_index_ >= chunk_end_; }
 
   /** Point to the next edge with the same source, return false if not found. */
   bool next_src() {
@@ -1237,6 +1235,9 @@ static inline Result<Edges> ConstructEdgesCollection(
   EdgeInfo edge_info;
   GAR_ASSIGN_OR_RAISE(edge_info,
                       graph_info.GetEdgeInfo(src_label, edge_label, dst_label));
+  if (!edge_info.ContainAdjList(adj_list_type)) {
+    return Status::Invalid("Invalid adj list type");
+  }
   switch (adj_list_type) {
   case AdjListType::ordered_by_source:
     return EdgesCollection<AdjListType::ordered_by_source>(

cpp/test/test_graph.cc

@@ -119,4 +119,26 @@ TEST_CASE("test_edges_collection", "[Slow]") {
   }
   std::cout << "edge_count=" << count2 << std::endl;
   REQUIRE(edges2.size() == count2);
+
+  // empty collection
+  auto expect3 = GAR_NAMESPACE::ConstructEdgesCollection(
+      graph_info, src_label, edge_label, dst_label,
+      GAR_NAMESPACE::AdjListType::unordered_by_source, 5, 5);
+  REQUIRE(!expect2.has_error());
+  auto& edges3 = std::get<GAR_NAMESPACE::EdgesCollection<
+      GAR_NAMESPACE::AdjListType::unordered_by_source>>(expect3.value());
+  auto end3 = edges3.end();
+  GAR_NAMESPACE::IdType count3 = 0;
+  for (auto it = edges3.begin(); it != end3; ++it) {
+    count3++;
+  }
+  std::cout << "edge_count=" << count3 << std::endl;
+  REQUIRE(count3 == 0);
+  REQUIRE(edges3.size() == 0);
+
+  // invalid adjlist type
+  auto expect4 = GAR_NAMESPACE::ConstructEdgesCollection(
+      graph_info, src_label, edge_label, dst_label,
+      GAR_NAMESPACE::AdjListType::unordered_by_dest);
+  REQUIRE(expect4.status().IsInvalid());
 }