Use static_cast, Fix unittest

paddle/framework/backward.cc

@@ -120,7 +120,7 @@ std::shared_ptr<OperatorBase> BackwardRecursive(
            OpRegistry::CreateOp(
                "add", {dup_outputs}, {name},
                {{"input_format",
-                 std::vector<int>{0, (int)dup_outputs.size()}}})});
+                 std::vector<int>{0, static_cast<int>(dup_outputs.size())}}})});
     }
 
     insert_position.sort(

paddle/framework/backward_test.cc

@@ -181,6 +181,8 @@ TEST(Backward, simple_op_not_need_grad) {
 
   auto no_input_gop = f::Backward(*fwd, {"X", "b"});
   ASSERT_NE(no_input_gop, nullptr);
+  ASSERT_TRUE(no_input_gop->IsNetOp());
+  ASSERT_EQ(0UL, std::static_pointer_cast<f::NetOp>(no_input_gop)->ops_.size());
 }
 
 TEST(Backward, net_fc_backward_normal) {