1. A die comprising test circuitry for testing the die and/or for testing, when the die is stacked, interconnections between the die and an adjacent die, the test circuitry comprising: a first input port configured to receive test stimuli; a first output port configured to send test responses, the first input port and the first output port being located at a same side of the die, wherein there is a data signal path within the die between the first input port and the first output port; at least one second output port configured to send test stimuli towards another die; and at least one second input port configured to receive test responses from the another die, wherein there is a data signal path within the die between the first input port and at least one of the second output ports, and wherein there is a data signal path within the die between at least one of the second input ports and the first output port.