diff --git a/src/cascade/dataflow/test_dataflow.py b/src/cascade/dataflow/test_dataflow.py
index 3b5cba3..1e29aad 100644
--- a/src/cascade/dataflow/test_dataflow.py
+++ b/src/cascade/dataflow/test_dataflow.py
@@ -1,5 +1,5 @@
 from typing import Any
-from cascade.dataflow.dataflow import DataFlow, Edge, Event, EventResult, InvokeMethod, OpNode
+from cascade.dataflow.dataflow import CollectNode, CollectTarget, DataFlow, Edge, Event, EventResult, InvokeMethod, OpNode
 from cascade.dataflow.operator import StatefulOperator
 
 class DummyUser:
@@ -79,9 +79,19 @@ def test_simple_df_propogation():
 def test_merge_df_propogation():
     df = DataFlow("user.buy_2_items")
     n0 = OpNode(DummyUser, InvokeMethod("buy_2_items_0"))
-    n1 = OpNode(DummyItem, InvokeMethod("get_price"))
-    n2 = OpNode(DummyItem, InvokeMethod("get_price"))
-    n3 = MergeNode()
+    n3 = CollectNode(assign_result_to="item_prices", read_results_from="item_price")
+    n1 = OpNode(
+        DummyItem, 
+        InvokeMethod("get_price"), 
+        assign_result_to="item_price", 
+        collect_target=CollectTarget(n3, 2, 0)
+    )
+    n2 = OpNode(
+        DummyItem, 
+        InvokeMethod("get_price"), 
+        assign_result_to="item_price", 
+        collect_target=CollectTarget(n3, 2, 1)
+    )
     n4 = OpNode(DummyUser, InvokeMethod("buy_2_items_1"))
     df.add_edge(Edge(n0, n1))
     df.add_edge(Edge(n0, n2))
diff --git a/test_programs/expected/checkout_two_items.py b/test_programs/expected/checkout_two_items.py
index c3784bd..2081cd3 100644
--- a/test_programs/expected/checkout_two_items.py
+++ b/test_programs/expected/checkout_two_items.py
@@ -1,17 +1,19 @@
 from typing import Any
-# from ..target.checkout_item import User, Item
-# from cascade.dataflow.dataflow import DataFlow, OpNode, InvokeMethod, Edge
+
+from cascade.dataflow.operator import StatefulOperator
+from ..target.checkout_two_items import User, Item
+from cascade.dataflow.dataflow import DataFlow, OpNode, InvokeMethod, Edge, CollectNode, CollectTarget
 
 def buy_two_items_0_compiled(variable_map: dict[str, Any], state: User, key_stack: list[str]) -> Any:
-    key_stack.append(variable_map['item_1_key'])
-    key_stack.append(variable_map['item_2_key'])
+    key_stack.append(
+        [variable_map["item1_key"], variable_map["item2_key"]]
+    )
     return None
 
-
 def buy_two_items_1_compiled(variable_map: dict[str, Any], state: User, key_stack: list[str]) -> Any:
     key_stack.pop()
-    item_price_1_0 = variable_map['item_price_1_0']
-    item_price_2_0 = variable_map['item_price_2_0']
+    item_price_1_0 = variable_map['item_price_1']
+    item_price_2_0 = variable_map['item_price_2']
     total_price_0 = item_price_1_0 + item_price_2_0
     state.balance -= total_price_0
     return state.balance >= 0
@@ -22,13 +24,67 @@ def get_price_0_compiled(variable_map: dict[str, Any], state: Item, key_stack: l
     return state.price
 
 
-def user_buy_item_df():
-    df = DataFlow("user.buy_item")
-    n0 = OpNode(User, InvokeMethod("buy_item_0"))
-    n1 = OpNode(Item, InvokeMethod("get_price"), assign_result_to="item_price")
-    n2 = OpNode(User, InvokeMethod("buy_item_1"))
+# An operator is defined by the underlying class and the functions that can be called
+user_op = StatefulOperator(
+    User, 
+    {
+        "buy_two_items_0": buy_two_items_0_compiled,
+        "buy_two_items_1": buy_two_items_1_compiled
+    }, 
+   None)
+
+item_op = StatefulOperator(
+    Item, {"get_price": get_price_0_compiled}, None
+)
+
+def user_buy_two_items_df():
+    df = DataFlow("user.buy_2_items")
+    n0 = OpNode(user_op, InvokeMethod("buy_2_items_0"))
+    n1 = OpNode(
+        item_op, 
+        InvokeMethod("get_price"), 
+        assign_result_to="item_price_1", 
+    )
+    n2 = OpNode(
+        item_op, 
+        InvokeMethod("get_price"), 
+        assign_result_to="item_price_2", 
+    )
+    n3 = OpNode(user_op, InvokeMethod("buy_2_items_1"))
     df.add_edge(Edge(n0, n1))
+    df.add_edge(Edge(n0, n2))
     df.add_edge(Edge(n1, n2))
+    df.add_edge(Edge(n2, n3))
+    df.entry = n0
+    return df
+
+
+# For future optimizations (not used)
+def user_buy_two_items_df_parallelized():
+    df = DataFlow("user.buy_2_items")
+    n0 = OpNode(user_op, InvokeMethod("buy_2_items_0"))
+    n3 = CollectNode(assign_result_to="item_prices", read_results_from="item_price")
+    n1 = OpNode(
+        item_op, 
+        InvokeMethod("get_price"), 
+        assign_result_to="item_price", 
+        collect_target=CollectTarget(n3, 2, 0)
+    )
+    n2 = OpNode(
+        item_op, 
+        InvokeMethod("get_price"), 
+        assign_result_to="item_price", 
+        collect_target=CollectTarget(n3, 2, 1)
+    )
+    n4 = OpNode(user_op, InvokeMethod("buy_2_items_1"))
+    df.add_edge(Edge(n0, n1))
+    df.add_edge(Edge(n0, n2))
+    df.add_edge(Edge(n1, n3))
+    df.add_edge(Edge(n2, n3))
+    df.add_edge(Edge(n3, n4))
     df.entry = n0
     return df
 
+user_op.dataflows =  {
+    "buy_two_items": user_buy_two_items_df(),
+}
\ No newline at end of file