refactor: use mempool::empty everywhere (#271)

Also impl with `Default`.

Co-Authored-By: Gilad Chase <gilad@starkware.com>

crates/gateway/src/gateway_test.rs

@@ -6,7 +6,7 @@ use axum::http::StatusCode;
 use axum::response::{IntoResponse, Response};
 use blockifier::context::ChainInfo;
 use blockifier::test_utils::CairoVersion;
-use rstest::rstest;
+use rstest::{fixture, rstest};
 use starknet_api::rpc_transaction::RPCTransaction;
 use starknet_api::transaction::TransactionHash;
 use starknet_mempool::communication::create_mempool_server;
@@ -28,6 +28,11 @@ use crate::utils::{external_tx_to_account_tx, get_tx_hash};
 
 const MEMPOOL_INVOCATIONS_QUEUE_SIZE: usize = 32;
 
+#[fixture]
+fn mempool() -> Mempool {
+    Mempool::empty()
+}
+
 pub fn app_state(
     mempool_client: SharedMempoolClient,
     state_reader_factory: TestStateReaderFactory,
@@ -67,10 +72,8 @@ pub fn app_state(
 async fn test_add_tx(
     #[case] tx: RPCTransaction,
     #[case] state_reader_factory: TestStateReaderFactory,
+    mempool: Mempool,
 ) {
-    // TODO: Add fixture.
-
-    let mempool = Mempool::new([]);
     // TODO(Tsabary): wrap creation of channels in dedicated functions, take channel capacity from
     // config.
     let (tx_mempool, rx_mempool) =

crates/mempool/src/mempool.rs

@@ -15,7 +15,7 @@ use crate::transaction_pool::TransactionPool;
 #[path = "mempool_test.rs"]
 pub mod mempool_test;
 
-#[derive(Debug)]
+#[derive(Debug, Default)]
 pub struct Mempool {
     // TODO: add docstring explaining visibility and coupling of the fields.
     txs_queue: TransactionPriorityQueue,
@@ -25,11 +25,7 @@ pub struct Mempool {
 
 impl Mempool {
     pub fn new(inputs: impl IntoIterator<Item = MempoolInput>) -> Self {
-        let mut mempool = Mempool {
-            txs_queue: TransactionPriorityQueue::default(),
-            tx_pool: TransactionPool::default(),
-            state: HashMap::default(),
-        };
+        let mut mempool = Mempool::empty();
 
         for MempoolInput { tx, account: Account { sender_address, state } } in inputs.into_iter() {
             // Attempts to insert a key-value pair into the mempool's state. Returns `None`
@@ -57,7 +53,7 @@ impl Mempool {
     }
 
     pub fn empty() -> Self {
-        Mempool::new([])
+        Mempool::default()
     }
 
     /// Retrieves up to `n_txs` transactions with the highest priority from the mempool.

crates/mempool/src/mempool_test.rs

@@ -44,7 +44,7 @@ macro_rules! add_tx_input {
 
 #[fixture]
 fn mempool() -> Mempool {
-    Mempool::new([])
+    Mempool::empty()
 }
 
 #[rstest]