test: add integration test for buy transaction reverting on insuffici…

creator-keys/tests/buy_insufficient_xlm_revert.rs

@@ -0,0 +1,41 @@
+//! Integration test for buy transaction reverting when buyer sends insufficient XLM / attached amount < current price.
+
+mod contract_test_env;
+
+use contract_test_env::{
+    capture_snapshot, compute_expected_buy_price, register_creator_keys, register_test_creator,
+    set_key_price_for_tests, test_env_with_auths,
+};
+use creator_keys::ContractError;
+use soroban_sdk::{testutils::Address as _, Address};
+
+#[test]
+fn test_buy_key_insufficient_xlm_reverts_without_state_mutation() {
+    let env = test_env_with_auths();
+    let (client, _) = register_creator_keys(&env);
+    let base_price = 100i128;
+    set_key_price_for_tests(&env, &client, base_price);
+
+    let creator = register_test_creator(&env, &client, "alice");
+    let buyer = Address::generate(&env);
+
+    let current_price = compute_expected_buy_price(0, base_price);
+    let insufficient_amount = current_price - 1;
+
+    let snapshot_before = capture_snapshot(&client, &creator, &buyer);
+    assert_eq!(client.get_total_key_supply(&creator), 0);
+    assert_eq!(client.get_key_balance(&creator, &buyer), 0);
+
+    // Invoke buy with attached amount 1 stroop below the current price
+    let result = client.try_buy_key(&creator, &buyer, &insufficient_amount, &None);
+
+    // Assert transaction reverts with InsufficientPayment error code
+    assert_eq!(result, Err(Ok(ContractError::InsufficientPayment)));
+
+    // Assert creator's key supply and buyer's holdings are unchanged after revert
+    let snapshot_after = capture_snapshot(&client, &creator, &buyer);
+    snapshot_before.assert_unchanged(&snapshot_after);
+
+    assert_eq!(client.get_total_key_supply(&creator), 0);
+    assert_eq!(client.get_key_balance(&creator, &buyer), 0);
+}