If you have had to purchase RAT tests to be able to work, you will be able to receive a tax deduction for the cost you have incurred from 1 July 2021 (you will need evidence of the expense). If the RAT test cost $20, someone on a marginal tax rate of 32.5% would receive a tax benefit of $6.50.
For business, it is expected that RAT, PCR and other coronavirus tests will be exempt from FBT from the 2021-2022 FBT year.
Having said that, it is important to note that the Australian Taxation Office (ATO) will be reviewing claims to determine if they are reasonable. For example, an individual who makes a large deduction claim for COVID-19 test expenses could come under scrutiny if they have been primarily working from home during the income year.