Provided is a device capable of generating test patterns even after the design stage. The area of a circuit which is included in the device and unnecessary during normal operation can be reduced. The device includes a first circuit and a second circuit. The second circuit includes a plurality of third circuits, a plurality of fourth circuits, and a fifth circuit and has a function of generating a signal for testing operation of the first circuit and a function of operating as part of the first circuit. The fourth circuit has a function of storing a first data and a function of storing a second data. The fifth circuit has a function of writing the first data to the plurality of fourth circuits, a function of writing the second data to the plurality of fourth circuits, and a function of reading the second data from the plurality of fourth circuits.