A processor acquires a plurality of test items for a simulation model of a target system, each test item including at least one event; detects a set of test items from the plurality of test items under an aggregation condition in which an event in the set is not dependent on an event in another test item in the set; includes a common event, which is an event in the set that is the same as an event in another test item in the set, in an aggregate test item while avoiding overlapping of the common event, and includes a unique event, which is an event in the set that differs from events in other test items in the set, in the aggregate test item; and executes a simulation using the simulation model in accordance with the aggregate test item.