Apparatus and methods are described for subsea control system testing including one or more of electrical, optical and fluidic conduit testing, wherein the testing is conducted subsea using a subsea testing skid. In one embodiment of the invention a subsea pipeline service skid is provided that includes at least one skid mounted pump dimensioned to deliver from about 3000 to about 20000 p.s.i. of pressure for pressure testing the fluidic conduits to desired pressures. Modular construction of the skid permits customization for testing service of unique subsea control equipment.