Criminals may want their work to be hidden. Tests cannot show that a program is correct. Suppose I change the software that selects people for a tax audit so that my number never comes up. Peer reviews efficiently detect errors like this in industry. Code review is a tool of the Open Source movement.
Peer reviews are even part of the academic life.
In a democracy, the people are the peers. Elitist programmers may argue that normal people cannot understand their code. However, I have found that all kinds of people can understand computers. Most can learn to understand code. Many discover the pleasure of finding errors and mistakes in it.