A testing device performing a worst case scenario test includes a machine learning device and the machine learning device observes data representing a test item and data representing an operation state and specifications of a manufacturing machine as state variables representing a current state of an environment. Further, the machine learning device acquires determination data representing a suitability determination result of an operation state of the manufacturing machine obtained when the test item is executed, and performs learning by using the state variables and the determination data in a state where manufacturing machine operation state data and manufacturing machine specification data are associated with test item data.