(27)In order to ensure that the risk management procedures of a CSD-banking service provider are sufficiently sound even in adverse conditions, the stress testing of the CSD-banking service provider's liquid financial resources should be rigorous and forward looking. For the same reason, tests should consider a range of extreme but plausible scenarios and be conducted for each relevant currency offered by the CSD-banking service provider taking into account the possible failure of one of the prearranged funding arrangements. Scenarios should include but not be limited to the default of two of the CSD-banking service provider's largest participants in that currency. This is necessary in order to establish a rule that is on the one hand prudent, as it takes into account the fact that other participants are also capable of generating liquidity risk, besides the largest one; and, on the other hand, a rule that is also proportionate to the objective, as it does not take into account those other participants that present a lesser potential for generating liquidity risk.