Adds Cheatcodes::AddAccount

core/src/environment/instruction.rs

@@ -223,6 +223,12 @@ pub enum Cheatcodes {
         /// The address of the account to fetch.
         address: ethers::types::Address,
     },
+    /// An `AddAccount` is used to add a default/unfunded account.
+    /// If the account exists, the value is updated.
+    AddAccount {
+        /// The address of the account to be added.
+        address: eAddress,
+    },
 }
 
 /// Wrapper around [`AccountState`] that can be serialized and deserialized.
@@ -264,4 +270,11 @@ pub enum CheatcodesReturn {
         /// Storage slots of the account.
         storage: HashMap<U256, U256>,
     },
+
+    /// A `AddAccount` returns nothing.
+    AddAccount {
+        /// Basic account information of inserted account like nonce, balance,
+        /// code hash, bytcode.
+        info: AccountInfo,
+    },
 }

core/src/environment/mod.rs

@@ -366,6 +366,7 @@ impl Environment {
                         }
                         Cheatcodes::Deal { address, amount } => {
                             let recast_address = Address::from(address.as_fixed_bytes());
+
                             match db.state.write()?.accounts.get_mut(&recast_address) {
                                 Some(account) => {
                                     account.info.balance += U256::from_limbs(amount.0);
@@ -408,6 +409,23 @@ impl Environment {
                                 }
                             }
                         }
+                        Cheatcodes::AddAccount { address } => {
+                            let recast_address = Address::from(address.as_fixed_bytes());
+
+                            let account = revm::db::DbAccount {
+                                info: AccountInfo::default(),
+                                account_state: AccountState::None,
+                                storage: HashMap::new(),
+                            };
+                            db.state
+                                .write()?
+                                .accounts
+                                .insert(recast_address, account.clone());
+
+                            outcome_sender.send(Ok(Outcome::CheatcodeReturn(
+                                CheatcodesReturn::AddAccount { info: account.info },
+                            )))?;
+                        }
                     },
                     // A `Call` is not state changing and will not create events but will create
                     // console logs.

core/tests/middleware_integration.rs

@@ -302,6 +302,47 @@ async fn deal_missing_account() {
     assert!(balance.is_err());
 }
 
+#[tokio::test]
+async fn add_account_cheatcode() {
+    let (_environment, client) = startup();
+
+    // First try to add balance to the non-existent new_address account
+    // It should faill
+    client
+        .apply_cheatcode(Cheatcodes::Deal {
+            address: client.default_sender().unwrap(),
+            amount: eU256::from(1),
+        })
+        .await
+        .unwrap();
+    let mut new_address = client.address().0;
+    new_address[0] = new_address[0].wrapping_add(1);
+    let new_address = eAddress::from(new_address);
+    let balance = client.get_balance(new_address, None).await;
+    assert!(balance.is_err());
+
+    // Then add the new_address account
+    client
+        .apply_cheatcode(Cheatcodes::AddAccount {
+            address: new_address,
+        })
+        .await
+        .unwrap();
+
+    // And fill it up
+    let new_balance = eU256::from(32);
+    client
+        .apply_cheatcode(Cheatcodes::Deal {
+            address: new_address,
+            amount: new_balance,
+        })
+        .await
+        .unwrap();
+
+    let balance = client.get_balance(new_address, None).await.unwrap();
+    assert_eq!(balance, new_balance);
+}
+
 #[tokio::test]
 async fn set_gas_price() {
     let (_environment, client) = startup();

docs/src/usage/arbiter_core/environment.md

@@ -66,6 +66,7 @@ fn main() {
 - `Instruction::Cheatcode`: Execute one of the `Cheatcodes` on the `Environment`'s world state. 
 The `Cheatcodes` include:
     - `Cheatcodes::Deal`: Used to set the raw ETH balance of a user. Useful when you need to pay gas fees in a transaction.
+    - `Cheatcodes::AddAccount`: Initializes a new default account if it doesn't exist.
     - `Cheatcodes::Load`: Gets the value of a storage slot of an account. 
     - `Cheatcodes::Store`: Sets the value of a storage slot of an account.
     - `Cheatcodes::Access`: Gets the account at an address.