The correct answer is D.

Deposit inflows are not typically considered in the assumptions for a liquidity stress test. Liquidity stress testing primarily focuses on potential scenarios that could lead to a liquidity crunch or shortfall. Therefore, the assumptions made during this process typically revolve around factors that could lead to a decrease in available liquidity. Deposit inflows, which represent an increase in available liquidity, are not typically considered in these assumptions. This is because the primary aim of liquidity stress testing is to assess the institution's ability to withstand scenarios where liquidity decreases, not increases.

Choice A is incorrect. Deposit outflows are a crucial assumption in liquidity stress testing. In times of financial stress, depositors may withdraw their funds, leading to a decrease in the institution's liquidity. Therefore, it is essential to consider potential deposit outflows during the process.

Choice B is incorrect. Investment portfolio haircuts are also typically considered during liquidity stress testing. A haircut refers to the reduction applied to the value of an institution's assets to account for potential losses that could occur if those assets had to be sold quickly (i.e., under stressed market conditions). This reduction can significantly impact an institution's available liquidity.

Choice C is incorrect. Collateral requirements are another important assumption in this process.