fix: Add Regression Tests for All Fixed Bugs

docs/regression-testing-policy.md

@@ -0,0 +1,18 @@
+# Regression Testing Policy
+
+- Every bug fix must include a failing regression test that reproduces the issue and passes with the fix.
+- Place new regression tests alongside the affected crate’s tests or under integration_tests in a dedicated regression_tests module.
+- Tests must be minimal, deterministic, and focus on the fixed behavior.
+- Do not modify production code solely to accommodate tests.
+- Link the test to its issue or PR number in the commit message.
+- CI must block merges for bug-fix PRs without a corresponding regression test.
+
+Scope
+- Applies to all crates in this workspace.
+- Includes unit, integration, and property-based tests where appropriate.
+
+Process
+- Reproduce: Write a test that fails against the buggy behavior.
+- Fix: Implement the code change.
+- Verify: Ensure the new test and the full suite pass locally and in CI.
+- Document: Reference the issue/PR in the test commit message.

integration_tests/tests/regression_tests.rs

@@ -0,0 +1,82 @@
+#![cfg(test)]
+
+use soroban_sdk::{testutils::Address as _, Address, Env, String as SorobanString};
+
+use bill_payments::{BillPayments, BillPaymentsClient};
+use insurance::{Insurance, InsuranceClient};
+use remittance_split::{RemittanceSplit, RemittanceSplitClient};
+
+mod regression_tests {
+    use super::*;
+
+    #[test]
+    #[should_panic(expected = "overflow")]
+    fn bill_payments_total_unpaid_overflow_panics() {
+        let env = Env::default();
+        env.mock_all_auths();
+        let contract_id = env.register_contract(None, BillPayments);
+        let client = BillPaymentsClient::new(&env, &contract_id);
+        let owner = Address::generate(&env);
+
+        let amount = i128::MAX / 2 + 1000;
+
+        client.create_bill(
+            &owner,
+            &SorobanString::from_str(&env, "Bill1"),
+            &amount,
+            &1_000_000u64,
+            &false,
+            &0u32,
+            &SorobanString::from_str(&env, "XLM"),
+        );
+
+        client.create_bill(
+            &owner,
+            &SorobanString::from_str(&env, "Bill2"),
+            &amount,
+            &1_000_000u64,
+            &false,
+            &0u32,
+            &SorobanString::from_str(&env, "XLM"),
+        );
+
+        let _ = client.get_total_unpaid(&owner);
+    }
+
+    #[test]
+    fn remittance_split_checked_arithmetic_overflow_returns_error() {
+        let env = Env::default();
+        env.mock_all_auths();
+        let contract_id = env.register_contract(None, RemittanceSplit);
+        let client = RemittanceSplitClient::new(&env, &contract_id);
+        let owner = Address::generate(&env);
+
+        client.initialize_split(&owner, &0u64, &50u32, &30u32, &15u32, &5u32);
+
+        let overflow_amount = i128::MAX / 50 + 1;
+        let result = client.try_calculate_split(&overflow_amount);
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn insurance_non_owner_cannot_pay_premium() {
+        let env = Env::default();
+        env.mock_all_auths();
+        let contract_id = env.register_contract(None, Insurance);
+        let client = InsuranceClient::new(&env, &contract_id);
+        let owner = Address::generate(&env);
+        let other = Address::generate(&env);
+
+        let policy_id = client.create_policy(
+            &owner,
+            &SorobanString::from_str(&env, "Policy"),
+            &SorobanString::from_str(&env, "health"),
+            &100i128,
+            &10_000i128,
+        );
+
+        let res = client.try_pay_premium(&other, &policy_id);
+        assert!(res.is_err());
+    }
+}
+