text: from stellar_sdk import Asset
  from stellar_sdk.call_builder.call_builder_async import OrderbookCallBuilder
  from tests.call_builder.call_builder_async import client, horizon_url
  
  
  class TestOrderbookCallBuilder:
      def test_init(self):
          selling = Asset(
              "BTC", "GATEMHCCKCY67ZUCKTROYN24ZYT5GK4EQZ65JJLDHKHRUZI3EUEKMTCH"
          )
          buying = Asset.native()
          builder = OrderbookCallBuilder(horizon_url, client, selling, buying)
          assert builder.endpoint == "order_book"
          assert builder.params == {
              "selling_asset_type": selling.type,
              "selling_asset_code": selling.code,
              "selling_asset_issuer": selling.issuer,
              "buying_asset_type": buying.type,
          }
  