A dominant white cat with blue eyes is said to be at high risk of being deaf. (Here the "dominant" refers to the white color gene, not behaviour.) In case of a white cat with odd eyes, the ear on the side with the blue eye may be deaf, though in some rare cases an odd-eyed cat can also be totally deaf.

That's one of the cats I have. Totally white fur, pink pads and ears, and odd eyes. I have tested her for hearing and it seems quite obvious that she can hear, but does she hear only with one ear or two? How would I test if she's deaf in the ear on the blue side?