The invention provides a test circuit for n input/output arrays. Each of the n input/output arrays has M pairs of input/output. The test circuit includes M write drivers and M comparing circuits. The ith write driver provides an ith test signal to the ith inputs of all of the n input/output arrays, and 1≦i≦M. The jth comparing circuit determines if jth output signals of all of the n input/output arrays are the same, and outputs a jth comparing result correspondingly, and 1≦j≦M. The invention also provides a method of testing n input/output arrays. The invention also provides a storage device.