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: mod.rs
    path of file: ./repos/solana/sdk/src/transaction
    
    the code of the file until where you have to start completion: //! Atomically-committed sequences of instructions.
//!
//! While [`Instruction`]s are the basic unit of computation in Solana, they are
//! submitted by clients in [`Transaction`]s containing one or more
//! instructions, and signed by one or more [`Signer`]s. Solana executes the
//! instructions in a transaction in order, and only commits any changes if all
//! instructions terminate without producing an error or exception.
//!
//! Transac
    
    fn test_unsized_signers() {
        fn instructions_to_tx(
            instructions: &[Instruction],
            signers: Box<dyn Signers>,
        ) -> Transaction {
            let pubkeys = signers.pubkeys();
            let first_signer = pubkeys.first().expect("should exist");
            let message = Message::new(instructions, Some(first_signer));
            Transaction::new(signers.as_ref(), message, Hash::default())
        }

        let signer: Box<dyn Signer> = Box::new(Keypair::new());
        let tx = instructions_to_tx(&[], Box::new(vec![signer]));

        assert!(tx.is_signed());
    }