my dd1 has had a few hearing tests.
she had the standard distraction tests with hv (at 9 months, i think, and at about 8 months). they did another one when she was 2 because she kept failing the distractio tests, or only just scraping through.
she got referred for a "proper" hearng test, which she had at 2.6, but she didn't co-operate.
she re-took the test at 3.6 ish (memory fails!) and passed.
the tests are not difficult, but do need a certain amount of co operation. dd1 is ASD, so co-ooperation isn't her strongest point.
in dd1's test, they got her playing with various things, then played a range of noises/frequencies/pitches behind herand noted when she noticed them.
they also did a pulse test - similar to the ones newborns have now, where a tone is played down the ear canal and the echo response measured (this is the bit she wouldn't co-operate for, as she had to wear something similar to in the ear headphones)
hth