test: add charge() insufficient-allowance error path test

contract/src/test.rs

@@ -1194,6 +1194,8 @@ 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
 // ─────────────────────────────────────────────────────────────
@@ -1285,3 +1287,34 @@ fn test_set_grace_period_emits_event() {
     assert_eq!(topic_symbol, Symbol::new(&env, "grace_period_updated"));
     assert_eq!(emitted_seconds, 7200u64);
 }
+
+// ─────────────────────────────────────────────
+// Issue #232: charge() insufficient-allowance error path
+// ─────────────────────────────────────────────
+
+/// If a user's token allowance drops below `sub.amount` between subscribe and
+/// charge time, `transfer_from` must fail and propagate the error.
+#[test]
+#[should_panic]
+fn test_charge_insufficient_allowance() {
+    let (env, contract_id, token_addr, user, merchant) = setup();
+    let client = FlowPayClient::new(&env, &contract_id);
+
+    let amount: i128 = 5_0000000;
+    let interval: u64 = 86400;
+
+    // Subscribe with sufficient allowance
+    client.subscribe(&user, &merchant, &amount, &interval, &token_addr, &None, &None);
+
+    // Revoke allowance — set it to 0
+    let token = TokenClient::new(&env, &token_addr);
+    token.approve(&user, &contract_id, &0, &200);
+
+    // Advance ledger past the interval
+    env.ledger().with_mut(|l| {
+        l.timestamp += interval + 1;
+    });
+
+    // charge() should panic because transfer_from fails with insufficient allowance
+    client.charge(&user);
+}