add SequenceLength test

tests/python/frontend/onnx/test_forward.py

@@ -7760,10 +7760,16 @@ def verify_sequence_ops(tensor_shape, num_tensors, axis=0, position=0, new_axis=
             "SplitToSequence", inputs=["concat_sequence"], outputs=["split_sequence"], axis=axis
         )
 
+        # Test tensor extraction from sequence
         at_node = helper.make_node(
             "SequenceAt", inputs=["split_sequence", "position"], outputs=["output"]
         )
 
+        # Test sequence length
+        split_node = helper.make_node(
+            "SequenceLength", inputs=["concat_sequence"], outputs=["output_2"]
+        )
+
         if new_axis is not None:
             new_axis_attr = helper.make_attribute("new_axis", new_axis)
             concat_node.attribute.append(new_axis_attr)
@@ -7781,7 +7787,8 @@ def verify_sequence_ops(tensor_shape, num_tensors, axis=0, position=0, new_axis=
             output_shape[axis] = num_tensors + 1
         else:
             output_shape[axis] = (num_tensors + 1) * output_shape[axis]
-        graph_outputs = [helper.make_tensor_value_info("output", TensorProto.FLOAT, output_shape)]
+        graph_outputs = [helper.make_tensor_value_info("output", TensorProto.FLOAT, output_shape),
+                         helper.make_tensor_value_info("output_2", TensorProto.INT, ())]
 
         graph_nodes = [position_node, construct_node, insert_node, concat_node, split_node, at_node]