test: add batch_charge large-list stress test

contract/src/test.rs

@@ -557,6 +557,37 @@ fn test_batch_charge_no_subscription() {
     assert_eq!(results.get(0).unwrap(), crate::ChargeResult::NoSubscription);
 }
 
+#[test]
+fn test_batch_charge_stress() {
+    let (env, contract_id, token_addr, _user, merchant) = setup();
+    let client = FlowPayClient::new(&env, &contract_id);
+    let token = TokenClient::new(&env, &token_addr);
+    let sac = StellarAssetClient::new(&env, &token_addr);
+
+    env.budget().reset_unlimited();
+
+    let num_users = 100;
+    let mut users = soroban_sdk::Vec::new(&env);
+    let interval = 86400;
+
+    for _ in 0..num_users {
+        let u = Address::generate(&env);
+        sac.mint(&u, &10_000_0000000);
+        token.approve(&u, &contract_id, &10_000_0000000, &200);
+        client.subscribe(&u, &merchant, &1_0000000, &interval, &token_addr, &None, &None);
+        users.push_back(u);
+    }
+
+    env.ledger().with_mut(|l| { l.timestamp += interval + 1; });
+
+    let results = client.batch_charge(&users);
+
+    assert_eq!(results.len(), num_users);
+    for r in results.into_iter() {
+        assert_eq!(r, crate::ChargeResult::Charged);
+    }
+}
+
 #[test]
 fn test_batch_charge_inactive() {
     let (env, contract_id, token_addr, user, merchant) = setup();
@@ -1194,6 +1225,7 @@ fn test_custom_sac_token_end_to_end_flow() {
     // Verify subscription is still active after pay_per_use
     let sub_final = client.get_subscription(&user).unwrap();
     assert!(sub_final.active, "subscription should remain active after pay_per_use");
+}
 // ─────────────────────────────────────────────────────────────
 // Issue #237: get_token() read function tests
 // ─────────────────────────────────────────────────────────────