add compound interest test (XRPLF#124)

* add compound interest test

* clang-format

src/test/app/XahauGenesis_test.cpp

@@ -1516,7 +1516,7 @@ struct XahauGenesis_test : public beast::unit_test::suite
     void testGovernanceL2(FeatureBitset features)
     {
         using namespace jtx;
-        testcase("Test governance membership voting L1");
+        testcase("Test governance membership voting L2");
 
         Env env{*this, envconfig(), features - featureXahauGenesis};
 
@@ -3846,6 +3846,99 @@ struct XahauGenesis_test : public beast::unit_test::suite
         env.close();
     }
 
+    void
+    testCompoundInterest(FeatureBitset features)
+    {
+        using namespace jtx;
+        using namespace std::chrono_literals;
+        testcase("test compound interest over 12 claims");
+
+        Env env{
+            *this, envconfig(), supported_amendments() - featureXahauGenesis};
+
+        double const rateDrops = 0.00333333333 * 1'000'000;
+        STAmount const feesXRP = XRP(1);
+
+        auto const user = Account("user");
+        env.fund(XRP(10000), user);
+        env.close();
+
+        // setup governance
+        auto const alice = Account("alice");
+        auto const bob = Account("bob");
+        auto const carol = Account("carol");
+        auto const david = Account("david");
+        auto const edward = Account("edward");
+
+        env.fund(XRP(10000), alice, bob, carol, david, edward);
+        env.close();
+
+        std::vector<AccountID> initial_members_ids{
+            alice.id(), bob.id(), carol.id(), david.id(), edward.id()};
+
+        setupGov(env, initial_members_ids);
+
+        // update reward delay
+        {
+            // this will be the new reward delay
+            // 100
+            std::vector<uint8_t> vote_data{
+                0x00U, 0x80U, 0xC6U, 0xA4U, 0x7EU, 0x8DU, 0x03U, 0x55U};
+
+            updateTopic(
+                env, alice, bob, carol, david, edward, 'R', 'D', vote_data);
+        }
+
+        // validate no unl report
+        BEAST_EXPECT(hasUNLReport(env) == false);
+
+        // opt in claim reward
+        env(claimReward(user, env.master), fee(XRP(1)), ter(tesSUCCESS));
+        env.close();
+
+        STAmount const begBal = env.balance(user);
+
+        for (int i = 0; i < 12; ++i)
+        {
+            // close ledgers
+            std::uint64_t ledgerDiff = 90 + (i * 30) + (i * 90);
+            validateTime(lastClose(env), ledgerDiff);
+            for (int i = 0; i < 5; ++i)
+            {
+                env.close(10s);
+            }
+            validateTime(lastClose(env), ledgerDiff + 90);
+
+            // define pre close values
+            STAmount const preUser = env.balance(user);
+            NetClock::time_point const preTime = lastClose(env);
+            std::uint32_t const preLedger = env.current()->seq();
+            auto const [acct, acctSle] = accountKeyAndSle(*env.current(), user);
+
+            // claim reward
+            env(claimReward(user, env.master), fee(feesXRP), ter(tesSUCCESS));
+            env.close();
+
+            // trigger emitted txn
+            env.close();
+
+            // calculate rewards
+            auto const netReward =
+                rewardUserAmount(*acctSle, preLedger, rateDrops);
+
+            // validate account fields
+            STAmount const postUser = preUser + netReward;
+            BEAST_EXPECT(expectAccountFields(
+                env, user, preLedger, preLedger + 1, postUser, preTime));
+        }
+
+        STAmount const endBal = env.balance(user);
+        auto const gainloss = ((endBal - begBal) / begBal);
+        std::uint64_t const asPercent =
+            static_cast<std::int64_t>(gainloss * 100);
+        BEAST_EXPECT(asPercent == 4);
+    }
+
     void
     testRewardHookWithFeats(FeatureBitset features)
     {   
@@ -3862,6 +3955,7 @@ struct XahauGenesis_test : public beast::unit_test::suite
         testValidElapsed1(features);
         testInvalidElapsed0(features);
         testInvalidElapsedNegative(features);
+        testCompoundInterest(features);
     }
 
     void