Add test for TopologicalSortPass on functions (#2198)

Add a test for `TopologicalSortPass` on functions in a model in
`onnxscript/ir/passes/common/topological_sort_test.py`.

* Add `test_topological_sort_on_functions` function to verify
`TopologicalSortPass` on functions.
* Create a function with unsorted nodes and a model containing the
function.
* Apply `TopologicalSortPass` and verify that the nodes in the function
are sorted correctly.

---

For more details, open the [Copilot Workspace
session](https://copilot-workspace.githubnext.com/microsoft/onnxscript/pull/2198?shareId=b8a28bde-b4e4-4037-9628-bf8c02bc144b).

Author: justinchuby

onnxscript/ir/passes/common/topological_sort_test.py

@@ -45,6 +45,41 @@ def test_topological_sort_modified_false(self):
             (self.node_a, self.node_b, self.node_c),
         )
 
+    def test_topological_sort_on_functions(self):
+        """Test that TopologicalSortPass works on functions in a model."""
+        # Create a function with unsorted nodes
+        func_graph = ir.Graph(
+            inputs=self.node_a.inputs,
+            outputs=self.node_c.outputs,
+            nodes=[self.node_c, self.node_b, self.node_a],  # Unsorted nodes
+        )
+        function = ir.Function(
+            domain="test_domain",
+            name="test_function",
+            graph=func_graph,
+            attributes=[],
+        )
+
+        # Create a model with the function
+        graph = ir.Graph(
+            inputs=[],
+            outputs=[],
+            nodes=[],
+            name="test_graph",
+        )
+        model = ir.Model(graph, ir_version=10, functions=[function])
+
+        # Apply the TopologicalSortPass
+        result = topological_sort.TopologicalSortPass()(model)
+
+        # Verify that the nodes in the function are sorted
+        sorted_func_nodes = (self.node_a, self.node_b, self.node_c)
+        self.assertTrue(result.modified)
+        self.assertEqual(
+            tuple(result.model.functions[function.identifier()]),
+            sorted_func_nodes,
+        )
+
 
 if __name__ == "__main__":
     unittest.main()