Title: test: add integration test for sell reverting when quantity exceeds holder balance

creator-keys/tests/sell_exceeds_balance.rs

@@ -0,0 +1,54 @@
+//! Integration test: sell reverts when holder has insufficient balance.
+
+mod contract_test_env;
+
+use contract_test_env::{
+    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, Env};
+
+fn setup(
+    env: &Env,
+) -> (
+    creator_keys::CreatorKeysContractClient<'_>,
+    Address,
+    Address,
+) {
+    let (client, _) = register_creator_keys(env);
+    set_key_price_for_tests(env, &client, 100_i128);
+    let creator = register_test_creator(env, &client, "alice");
+    let holder = Address::generate(env);
+    (client, creator, holder)
+}
+
+#[test]
+fn test_sell_exceeds_balance_reverts_insufficient_balance() {
+    let env = test_env_with_auths();
+    let (client, creator, holder) = setup(&env);
+
+    // Buy exactly 2 keys
+    client.buy_key(&creator, &holder, &100_i128, &None);
+    client.buy_key(&creator, &holder, &100_i128, &None);
+
+    assert_eq!(client.get_key_balance(&creator, &holder), 2);
+    let supply_before = client.get_total_key_supply(&creator);
+
+    // Sell all 2 keys - succeeds
+    client.sell_key(&creator, &holder, &None);
+    assert_eq!(client.get_key_balance(&creator, &holder), 0);
+
+    // Try to sell again with no keys - must revert
+    let result = client.try_sell_key(&creator, &holder, &None);
+
+    assert!(result.is_err());
+    match result {
+        Err(Ok(ContractError::InsufficientBalance)) => {}
+        other => panic!("expected InsufficientBalance, got {:?}", other),
+    }
+
+    // Holder still owns exactly 0 keys
+    assert_eq!(client.get_key_balance(&creator, &holder), 0);
+    // Creator supply decreased by 2 (from first successful sell)
+    assert_eq!(client.get_total_key_supply(&creator), supply_before - 2);
+}