Add unit tests

test/LaunchAuctionPriceOracle/DecayedPremium.t.sol

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+//SPDX-License-Identifier: MIT
+pragma solidity ~0.8.17;
+
+import {Test} from "forge-std/Test.sol";
+import {LaunchAuctionPriceOracleBase} from "./LaunchAuctionPriceOracleBase.t.sol";
+import {FixedPointMathLib} from "solady/utils/FixedPointMathLib.sol";
+
+contract DecayedPremium is LaunchAuctionPriceOracleBase {
+    function test_decayedPremium_zeroElapsed() public view {
+        uint256 elapsed = 0;
+        uint256 expectedPremium = startPremium;
+        uint256 actualPremium = oracle.decayedPremium(elapsed);
+        assertEq(actualPremium, expectedPremium);
+    }
+
+    function test_decayedPremium_boundaryConditions() public view {
+        uint256 zeroElapsedPremium = oracle.decayedPremium(0);
+        assertEq(zeroElapsedPremium, startPremium);
+
+        uint256 auctionEndPremium = oracle.decayedPremium(totalDays * 1 days);
+        assertTrue(auctionEndPremium < oracle.endValue());
+    }
+
+    function test_decayedPremium_halfPeriod() public view {
+        uint256 elapsed = 1 hours / 2;
+        uint256 expectedPremium = 70710678118654752400; // Calculated expected value for premium price after 1/2 day
+        uint256 actualPremium = oracle.decayedPremium(elapsed);
+        assertEq(actualPremium, expectedPremium);
+    }
+
+    function test_decayedPremium_threePeriods() public view {
+        uint256 elapsed = 3 hours;
+        uint256 expectedPremium = 12499999999999999900; // Calculated expected value for premium price after 3 days
+        uint256 actualPremium = oracle.decayedPremium(elapsed);
+        assertEq(actualPremium, expectedPremium);
+    }
+}

test/LaunchAuctionPriceOracle/ExponentialPremiumFuzzTest.t.sol

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+//SPDX-License-Identifier: MIT
+pragma solidity ~0.8.17;
+
+import {Test, console} from "forge-std/Test.sol";
+import {LaunchAuctionPriceOracleBase} from "./LaunchAuctionPriceOracleBase.t.sol";
+import {FixedPointMathLib} from "solady/utils/FixedPointMathLib.sol";
+
+contract ExponentialPremiumFuzzTest is LaunchAuctionPriceOracleBase {
+    function test_decayedPremium_decreasingPrices(uint256 elapsed) public view {
+        elapsed = bound(elapsed, 0, totalDays * 1 days);
+        uint256 actualPremium = oracle.decayedPremium(elapsed);
+        assert(actualPremium <= startPremium);
+    }
+
+    function test_decayedPremium_alwaysDecreasing(uint256 elapsed1, uint256 elapsed2) public view {
+        vm.assume(elapsed1 < elapsed2 && (elapsed1 < totalDays * 1 days));
+        elapsed1 = bound(elapsed1, 0, elapsed2);
+        elapsed2 = bound(elapsed2, elapsed1, totalDays * 1 days);
+
+        uint256 premium1 = oracle.decayedPremium(elapsed1);
+        uint256 premium2 = oracle.decayedPremium(elapsed2);
+
+        assert(premium1 >= premium2);
+    }
+}

test/LaunchAuctionPriceOracle/LaunchAuctionPriceOracleBase.t.sol

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+//SPDX-License-Identifier: MIT
+pragma solidity ^0.8.17;
+
+import {Test} from "forge-std/Test.sol";
+import {StablePriceOracle} from "src/L2/StablePriceOracle.sol";
+import {LaunchAuctionPriceOracle} from "src/L2/LaunchAuctionPriceOracle.sol";
+
+contract LaunchAuctionPriceOracleBase is Test {
+    LaunchAuctionPriceOracle oracle;
+
+    uint256 rent1;
+    uint256 rent2;
+    uint256 rent3;
+    uint256 rent4;
+    uint256 rent5;
+    uint256 rent10;
+
+    uint256 startPremium = 100 ether;
+    uint256 totalDays = 1;
+
+    uint256 hoursPerDay = 24;
+
+    function setUp() public {
+        uint256[] memory rentPrices = new uint256[](6);
+
+        rent1 = 316_808_781_402;
+        rent2 = 31_680_878_140;
+        rent3 = 3_168_087_814;
+        rent4 = 316_808_781;
+        rent5 = 31_680_878;
+        rent10 = 3_168_087; // 3,168,808.781402895 = 1e14 / (365.25 * 24 * 3600)
+
+        rentPrices[0] = rent1;
+        rentPrices[1] = rent2;
+        rentPrices[2] = rent3;
+        rentPrices[3] = rent4;
+        rentPrices[4] = rent5;
+        rentPrices[5] = rent10;
+
+        oracle = new LaunchAuctionPriceOracle(rentPrices, startPremium, totalDays);
+    }
+
+    function test_constructor() public view {
+        assertEq(oracle.startPremium(), startPremium);
+        assertEq(oracle.endValue(), startPremium >> (totalDays * hoursPerDay));
+        assertEq(oracle.price1Letter(), rent1);
+        assertEq(oracle.price2Letter(), rent2);
+        assertEq(oracle.price3Letter(), rent3);
+        assertEq(oracle.price4Letter(), rent4);
+        assertEq(oracle.price5Letter(), rent5);
+        assertEq(oracle.price10Letter(), rent10);
+    }
+}