You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: lib.rs
    path of file: ./repos/ink/integration-tests/e2e-runtime-only-backend
    
    the code of the file until where you have to start completion: #![cfg_attr(not(feature = "std"), no_std, no_main)]

#[ink::contract]
pub mod flipper {
    #[ink(storage)]
    pub struct Flipper {
        value: bool,
    }

    impl Flipper {
        
    
        async fn custom_runtime<Client: E2EBackend>(mut client: Client) -> E2EResult<()> {
            client
                .instantiate(
                    "e2e-runtime-only-backend",
                    &ink_e2e::alice(),
                    &mut FlipperRef::new(false),
                )
                .submit()
                .await
                .expect("instantiate failed");

            Ok(())
        }