add test cases to check the original timeline not changed

Author: rameshm

src/opentimelineio/stackAlgorithm.cpp

@@ -74,9 +74,10 @@ _flatten_next_item(
     }
 
     auto children = track->children();
-    for (int i = 0; i < children.size(); i++)
+    int children_size = static_cast<int>(children.size());
+    for (int i = 0; i < children_size; i++)
     {
-        std::optional<TimeRange> trim = std::nullopt;;
+        std::optional<TimeRange> trim = std::nullopt;
         SerializableObject::Retainer<Composable> child = children[i];
 
         // combine all non visible children into one continuous range
@@ -102,7 +103,7 @@ _flatten_next_item(
                 trim = child_trim;
             }
 
-            if (i+1 < children.size())
+            if (i+1 < children_size)
             {
                 child = children[i++];
             }

tests/test_stack_algo.cpp

@@ -259,6 +259,9 @@ main(int argc, char** argv)
         assertEqual(result->children().size(), 1);
         assertEqual(result->children()[0]->name(), std::string("track2_C"));
         assertEqual(result->duration().value(), 300);
+        assertEqual(st->children().size(), 2);
+        assertEqual(dynamic_cast<otio::Track*>(st->children()[0].value)->children().size(), 1);
+        assertEqual(dynamic_cast<otio::Track*>(st->children()[1].value)->children().size(), 2);
     });
 
     tests.add_test(
@@ -309,8 +312,11 @@ main(int argc, char** argv)
         assertEqual(result->children()[0]->name(), std::string("track2_C"));
         assertEqual(result->children()[1]->name(), std::string("track2_D"));
         assertEqual(result->duration().value(), 300);
+        assertEqual(st->children().size(), 2);
+        assertEqual(dynamic_cast<otio::Track*>(st->children()[0].value)->children().size(), 2);
+        assertEqual(dynamic_cast<otio::Track*>(st->children()[1].value)->children().size(), 2);
     });
 
     tests.run(argc, argv);
     return 0;
-}
+}