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test: verify the rounding behavior of equal-asset AMM deposits (#4982)

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* Specifically, test using tfLPToken flag
This commit is contained in:
Chenna Keshava B S
2024-04-18 13:15:31 -07:00
committed by GitHub
parent 24a275ba25
commit df3aa84523
1 changed files with 56 additions and 0 deletions
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56
src/test/app/AMM_test.cpp
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@@ -1244,6 +1244,62 @@ private:
expectLedgerEntryRoot(env, carol, XRPAmount{28'999'999'990}));
});
// equal asset deposit: unit test to exercise the rounding-down of
// LPTokens in the AMMHelpers.cpp: adjustLPTokens calculations
// The LPTokens need to have 16 significant digits and a fractional part
for (const Number deltaLPTokens :
{Number{UINT64_C(100000'0000000009), -10},
Number{UINT64_C(100000'0000000001), -10}})
{
testAMM([&](AMM& ammAlice, Env& env) {
// initial LPToken balance
IOUAmount const initLPToken = ammAlice.getLPTokensBalance();
const IOUAmount newLPTokens{
deltaLPTokens.mantissa(), deltaLPTokens.exponent()};
// carol performs a two-asset deposit
ammAlice.deposit(
DepositArg{.account = carol, .tokens = newLPTokens});
IOUAmount const finalLPToken = ammAlice.getLPTokensBalance();
// Change in behavior due to rounding down of LPTokens:
// there is a decrease in the observed return of LPTokens --
// Inputs Number{UINT64_C(100000'0000000001), -10} and
// Number{UINT64_C(100000'0000000009), -10} are both rounded
// down to 1e5
BEAST_EXPECT((finalLPToken - initLPToken == IOUAmount{1, 5}));
BEAST_EXPECT(finalLPToken - initLPToken < deltaLPTokens);
// fraction of newLPTokens/(existing LPToken balance). The
// existing LPToken balance is 1e7
const Number fr = deltaLPTokens / 1e7;
// The below equations are based on Equation 1, 2 from XLS-30d
// specification, Section: 2.3.1.2
const Number deltaXRP = fr * 1e10;
const Number deltaUSD = fr * 1e4;
const STAmount depositUSD =
STAmount{USD, deltaUSD.mantissa(), deltaUSD.exponent()};
const STAmount depositXRP =
STAmount{XRP, deltaXRP.mantissa(), deltaXRP.exponent()};
// initial LPTokens (1e7) + newLPTokens
BEAST_EXPECT(ammAlice.expectBalances(
XRP(10'000) + depositXRP,
USD(10'000) + depositUSD,
IOUAmount{1, 7} + newLPTokens));
// 30,000 less deposited depositUSD
BEAST_EXPECT(expectLine(env, carol, USD(30'000) - depositUSD));
// 30,000 less deposited depositXRP and 10 drops tx fee
BEAST_EXPECT(expectLedgerEntryRoot(
env, carol, XRP(30'000) - depositXRP - txfee(env, 1)));
});
}
// Equal limit deposit: deposit USD100 and XRP proportionally
// to the pool composition not to exceed 100XRP. If the amount
// exceeds 100XRP then deposit 100XRP and USD proportionally