I guess the boatyard won't test them on the boats because most are often located in ridiculously stupid and confined spaces, like under the after deck with only a couple or few inches clearance above them, which means fooling around getting bent up like the letter Z getting in there, trying to get the tops off, fooling about with a mirror, dipstick, trying to get a hydrometer or whatever tester in there. You can end up all distorted, broken, bruised, pins and needles, excruciating cramps, watery eyes, filthy, dizzy with hydrogen fumes, a burnt and bistered bum with crouching on the engine. To emerge completely disorientated, throwing up and with your clothes falling apart and disappearing off you with acid attack.