A device is disclosed for testing a memory, and the memory includes a first memory circuit and a second memory circuit. The second memory circuit is configured to store a first response of the first memory circuit. The device includes a comparing circuit and a calculating circuit. The comparing circuit is configured to compare the first response stored in the second memory circuit with a plurality of responses of the first memory circuit operated in conditions that are different from each other, to generate a plurality of first comparing results. The calculating circuit is configured to output, according to the plurality of first comparing results, a maximum hamming distance between two of the first responses and the plurality of responses of the first memory circuit.