diff --git a/runtime/src/bank_client.rs b/runtime/src/bank_client.rs
new file mode 100644
index 0000000000..7c5615e610
--- /dev/null
+++ b/runtime/src/bank_client.rs
@@ -0,0 +1,19 @@
+use crate::bank::Bank;
+use solana_sdk::signature::Keypair;
+use solana_sdk::transaction::{Transaction, TransactionError};
+
+pub struct BankClient<'a> {
+    bank: &'a Bank,
+    keypair: Keypair,
+}
+
+impl<'a> BankClient<'a> {
+    pub fn new(bank: &'a Bank, keypair: Keypair) -> Self {
+        Self { bank, keypair }
+    }
+
+    pub fn process_transaction(&self, tx: &mut Transaction) -> Result<(), TransactionError> {
+        tx.sign(&[&self.keypair], self.bank.last_blockhash());
+        self.bank.process_transaction(tx)
+    }
+}
diff --git a/runtime/src/lib.rs b/runtime/src/lib.rs
index 2ce51a1f93..674dfa90d4 100644
--- a/runtime/src/lib.rs
+++ b/runtime/src/lib.rs
@@ -1,6 +1,7 @@
 mod accounts;
 pub mod append_vec;
 pub mod bank;
+pub mod bank_client;
 mod blockhash_queue;
 pub mod bloom;
 pub mod loader_utils;
diff --git a/runtime/tests/system.rs b/runtime/tests/system.rs
index c91528cb55..8d7fcaaac3 100644
--- a/runtime/tests/system.rs
+++ b/runtime/tests/system.rs
@@ -1,44 +1,28 @@
 use solana_runtime::bank::Bank;
+use solana_runtime::bank_client::BankClient;
 use solana_sdk::genesis_block::GenesisBlock;
 use solana_sdk::native_program::ProgramError;
 use solana_sdk::signature::{Keypair, KeypairUtil};
 use solana_sdk::system_instruction::SystemInstruction;
 use solana_sdk::system_program;
-use solana_sdk::transaction::{InstructionError, Transaction, TransactionError};
+use solana_sdk::transaction::{InstructionError, TransactionError};
 use solana_sdk::transaction_builder::{BuilderInstruction, TransactionBuilder};
 
-struct SystemClient<'a> {
-    bank: &'a Bank,
-    keypair: Keypair,
-}
-
-impl<'a> SystemClient<'a> {
-    fn new(bank: &'a Bank, keypair: Keypair) -> Self {
-        bank.add_native_program("solana_system_program", &system_program::id());
-        Self { bank, keypair }
-    }
-
-    fn process_transaction(&self, mut tx: Transaction) -> Result<(), TransactionError> {
-        tx.sign_unchecked(&[&self.keypair], self.bank.last_blockhash());
-        self.bank.process_transaction(&tx)
-    }
-}
-
 #[test]
 fn test_system_unsigned_transaction() {
     let (genesis_block, from_keypair) = GenesisBlock::new(100);
     let bank = Bank::new(&genesis_block);
     let from_pubkey = from_keypair.pubkey();
-    let alice_client = SystemClient::new(&bank, from_keypair);
+    let alice_client = BankClient::new(&bank, from_keypair);
 
     let to_keypair = Keypair::new();
-    let to_pubkey = Keypair::new().pubkey();
-    let mallory_client = SystemClient::new(&bank, to_keypair);
+    let to_pubkey = to_keypair.pubkey();
+    let mallory_client = BankClient::new(&bank, to_keypair);
 
     // Fund to account to bypass AccountNotFound error
     let ix = SystemInstruction::new_move(&from_pubkey, &to_pubkey, 50);
-    let tx = TransactionBuilder::new_singleton(ix);
-    alice_client.process_transaction(tx).unwrap();
+    let mut tx = TransactionBuilder::new_singleton(ix);
+    alice_client.process_transaction(&mut tx).unwrap();
 
     // Erroneously sign transaction with recipient account key
     // No signature case is tested by bank `test_zero_signatures()`
@@ -47,9 +31,9 @@ fn test_system_unsigned_transaction() {
         &SystemInstruction::Move { lamports: 10 },
         vec![(from_pubkey, false), (to_pubkey, true)],
     );
-    let tx = TransactionBuilder::new_singleton(ix);
+    let mut tx = TransactionBuilder::new_singleton(ix);
     assert_eq!(
-        mallory_client.process_transaction(tx),
+        mallory_client.process_transaction(&mut tx),
         Err(TransactionError::InstructionError(
             0,
             InstructionError::ProgramError(ProgramError::MissingRequiredSignature)