The determination of whether an activity is “regularly carried on” is generally a fact and circumstances test and is based on the particular facts of the transaction or set of transactions during the year.

I’m in Arizona and I’m looking into a home that may have lead based paint, built in 1961 but not tested, I’ve heard about getting a home certified for lead/removing it.

I have 21 years in DOD/USAF, 7 of which was doing Logistic, Test Management, and Program Management of Multi-Million dollar acquisition, product support, and integration/modifications of a vast range of different Programs for the USAF. 

It took me about a week to get my license, start to finish- education, testing, forms, etc.

If OP elects de minimis safe harbor ("DMSH"), he's going to have to capitalize as the expenditure is going to be more than $2,500.If OP forgoes the DMSH and instead applies the Betterment, Adaptation, and Restoration tests ("BAR tests") under the tangible property regs, we'd almost certainly have a betterment and/or restoration of the HVAC subsystem on our hands, so we'd also capitalize under this option.OP may be able to use the safe harbor for small taxpayers ("SHST") to expense the costs, however not enough information was given by OP.If SHST is off the table due to limitation, then must capitalize. 

Inspection report tests prove it is in fact black mold but bc its in the corner and the connecting wall is finished we cant see if its spread. 2.

how to test this idea? 

Depending on what county you are in my answer can change but with the sympathetic press tenants are getting these days and the bad press landlords are getting I would not test my luck in legal cases right now. 

Those are subject to the FHA Self Sufficientcy test which virtually none will meet.

However now, all tenants are required to apply for assistance, or the landlord can do it for them, but if they don't get it in 14 days, you can evict them (we have not tested that last part).