Answer

Whilst I can certainly understand why you have asked this question, there is in fact a very good reason why most hearing tests are conducted in very quiet environments.  Whilst there are many types of hearing test, the most usual is used to find hearing thresholds, normally called an audiogram.  The threshold of hearing is the faintest sound which can be heard over a range of frequencies and both by air and bone conduction methods. The results indicate the extent of any hearing loss and usually identify the part of the auditory system which has been affected. The environment must be controlled to ensure the accuracy of the tests and fluctuating levels of background noise would invalidate the results.

Some hearing tests are conducted in the presence of noise but the source of the noise is usually a recording. Such tests normally are used to assess speech understanding in noise for comparison with speech understanding in quiet. Hearing aids are often assessed by a comparison of results in both quiet and noisy conditions. However, in order to establish hearing sensitivity levels and to be able to compare test results taken at intervals, very quiet conditions are essential.