testReturnJumps asserts the wrong ratio direction

Summary

testReturnJumps asserts currentReturn / previousReturn ~= 1.025, but the actual ratio is ~0.975 since higher tick means higher price and lower return. The test only passes due to the 10% tolerance.

Vulnerability Detail

In TickLibTest.sol#L33:

function testReturnJumps() public pure {
    for (uint256 i = 220; i <= 770; i++) {
        uint256 previousReturn = _return(TickLib.tickToPrice(i - 1));
        uint256 currentReturn = _return(TickLib.tickToPrice(i));
        assertApproxEqRel(
            currentReturn.mulDivDown(1e18, previousReturn), 1.025e18, 0.1e18, ...
        );
    }
}

_return(price) = 1e18 / price - 1, which is 1/price - 1. Since tickToPrice is monotonically increasing, a higher tick gives a higher price and a lower return. Therefore currentReturn / previousReturn = 1/1.025 ~= 0.9756, not 1.025.

The assertion passes because |0.9756 - 1.025| / 1.025 ~= 4.8%, which is within the 10% relative tolerance.

Impact

The test does not verify what it intends to. The expected value should be ~0.9756e18 (i.e. 1/1.025), or the ratio should be flipped to previousReturn / currentReturn.

Code Snippet

https://github.com/sherlock-audit/2026-04-morpho-midnight-apr-6th-2026/blob/main/morpho-org__midnight/test/TickLibTest.sol#L28-L36

Tool Used

Manual Review

Recommendation

Fix the assertion to check the correct ratio:

assertApproxEqRel(
    previousReturn.mulDivDown(1e18, currentReturn), 1.025e18, 0.01e18, ...
);