An apparatus and method for integrated serial bus testing in a data processing system are implemented. During testing of the data processing system, serial bus test signals are provided via a predetermined input/output (I/O) device port. Switching circuitry decouples I/O device control circuitry from the I/O port in response to a control signal having a first predetermined value. The switching circuitry additionally decouples the serial bus controller from the serial bus interface which fans out the serial data lines to serial peripheral devices. During operation of the data processing system, the switching circuitry couples the serial bus controller to the interface, couples the I/O device controller to the I/O device port, and decouples the serial interface from the I/O device port, in response to the control signal having a second predetermined value.