A method of testing gears, said method comprising: providing a first member of a gearset, said first member having a plurality of tooth flank surfaces, providing a second member of said gearset, said second member having a plurality of tooth flank surfaces, rolling said first member of said gearset in mesh with said second member of said gearset via rotating spindles (7, 8), applying a contrast agent comprising a luminescent agent which is mixed with a transmission oil to the tooth flank surfaces of at least one of the first and second members of said gearset during said rolling, stopping said applying and continuing with said rolling for multiple revolutions without fresh oil mixture supply, wherein as a result of the continued rolling after stopping the applying, the contrast agent is removed from applied areas on tooth flank surfaces of at least one of the first and second members where tooth flank surfaces of the first member contact tooth flank surfaces of the second member by being pressed away from the contact area, the contrast agent remaining in the area surrounding the contact area thereby resulting in a contact pattern being revealed on the tooth flank surfaces of at least one of the first and second gearset members, said contact pattern being indicative of the contact area between meshing tooth flank surfaces of the first and second members of the gearset, wherein, after full stop and withdrawal of the spindles to separate first and second gear member, said contact area is revealed by illuminating a single flank surface or a plurality of tooth flank surfaces of at least one of the first and second gearset members in a defined rotational position with ultra-violet light. providing a first member of a gearset, said first member having a plurality of tooth flank surfaces, providing a second member of said gearset, said second member having a plurality of tooth flank surfaces, rolling said first member of said gearset in mesh with said second member of said gearset via rotating spindles (7, 8), applying a contrast agent comprising a luminescent agent which is mixed with a transmission oil to the tooth flank surfaces of at least one of the first and second members of said gearset during said rolling, stopping said applying and continuing with said rolling for multiple revolutions without fresh oil mixture supply, wherein as a result of the continued rolling after stopping the applying, the contrast agent is removed from applied areas on tooth flank surfaces of at least one of the first and second members where tooth flank surfaces of the first member contact tooth flank surfaces of the second member by being pressed away from the contact area, the contrast agent remaining in the area surrounding the contact area thereby resulting in a contact pattern being revealed on the tooth flank surfaces of at least one of the first and second gearset members, said contact pattern being indicative of the contact area between meshing tooth flank surfaces of the first and second members of the gearset, wherein, after full stop and withdrawal of the spindles to separate first and second gear member, said contact area is revealed by illuminating a single flank surface or a plurality of tooth flank surfaces of at least one of the first and second gearset members in a defined rotational position with ultra-violet light.