Legitimacy to Test An Application Domain

12 years ago when I have trained a group of testers for one of the banks, a guy stood up in the middle of my testing course, and told me: "Do you have an economics degree?". "No." I have answered, and he continued: "Do you have any formal education in Finance at all?". "No." I have answered, "not formal". Then he said:" Then why should I give you a job testing my financial systems?".

That was a legitimate question, and on the break I have answer that "I do not have a financial degree or any formal finance background, but I have tested such systems (as they have) in two different banks in the last 2 years. That answer satisfied him well.

My point is that we are asked to test complex application domain systems, and sometimes (or many times) without the domain knowledge. Is that legitimate from a company to hire only testers with domain knowledge? or it is not? Can we test well enough, while not possessing the domain knowledge?

Let's take as example. A health care machine like CT, that has an analysis module analyzing the brain slices (pictures) - is that OK to test without being a doctor? I mean the user is a doctor, and we always take the user point of view in our end to end testing.

And, it experience is accounted for, like in my example, than when can we have the first experience?

Life tought me that the simple dynamics is that within a team there is at least one person that knows alot on the application domain, and a few others that learn from him/her. That is the case in most projects I have encountered. Some companies would not hire a tester, but rather hire someone that possesses the skills of the specific applcation domain (i.g. flight engineer, pilot, etc') and train him/her in testing skills.

I guess to summarize the discussion - it depends on the application domain and on the complexity of the system or type of system we must test. The fact that lives are at stake (mission-critic systems) could matter as well for making a decision as a test manager of that company.