A universal tester (100, 300, 400) comprising: a host interface slot configured to be connected to a first pluggable host card during an electrical test mode of operation to provide a stressed electrical signal to a host under test; the host interface slot being configured to be connected to a second pluggable host card during an optical test mode of operation, the second pluggable host card including an electrical-optical conversion block to convert a stressed electrical signal to a stressed optical signal that is provided to a host under test; and a stressor generator (114A, 1148) coupled to a first connector (128, 130) and to the host interface slot, the stressor generator (114A, 114B) being configured to receive an electrical signal from the first connector (128, 130) and generate the stressed electrical signal that simulates changes that may occur to a signal during transmission and is output to the host interface slot and transmitted to the host during a pass-through mode for the stressor generator (114A, 114B), the stressor generator (114A, 114B) being also configured to receive an electrical signal, generated by a host, from the host interface slot and generate the stressed electrical signal that simulates changes that may occur to a signal during transmission and is output to the host interface slot and transmitted to the host during a loop-back mode for the stressor generator (114A, 114B). a host interface slot configured to be connected to a first pluggable host card during an electrical test mode of operation to provide a stressed electrical signal to a host under test; the host interface slot being configured to be connected to a second pluggable host card during an optical test mode of operation, the second pluggable host card including an electrical-optical conversion block to convert a stressed electrical signal to a stressed optical signal that is provided to a host under test; and a stressor generator (114A, 1148) coupled to a first connector (128, 130) and to the host interface slot, the stressor generator (114A, 114B) being configured to receive an electrical signal from the first connector (128, 130) and generate the stressed electrical signal that simulates changes that may occur to a signal during transmission and is output to the host interface slot and transmitted to the host during a pass-through mode for the stressor generator (114A, 114B), the stressor generator (114A, 114B) being also configured to receive an electrical signal, generated by a host, from the host interface slot and generate the stressor generator (114A, 114B) being configured to receive an electrical signal from the first connector (128, 130) and generate the stressed electrical signal that simulates changes that may occur to a signal during transmission and is output to the host interface slot and transmitted to the host during a pass-through mode for the stressor generator (114A, 114B), the stressor generator (114A, 114B) being also configured to receive an electrical signal, generated by a host, from the host interface slot and generate the stressed electrical signal that simulates changes that may occur to a signal during transmission and is output to the host interface slot and transmitted to the host during a loop-back mode for the stressor generator (114A, 114B).