What will cost to test an app?

I'm a new grad student, recently I'm developing an iOS app and learning the software development life cycle. To test my app, I'm going to use testFlight.

I'm curious about what will cost when we are testing an app? Based on the knowledge I learnt, we will do different type of testing to eliminate bugs as much as possible, such as unit testing, Black-Box testing, White-Box testing, performance testing and so on. However, when we are doing those testing, what will cost the company in real developing environment? Do we have other factors that would affect our testing process?

I mean, what should a company add in their budget list and prepare before they start doing testing?

What will cost if using testFlight to test an iOS app?