I'll claim the only universal truth in programming as in anything is: "moderation", and it's corollary, "there is no silver bullet". They are all rules of thumb, and knowing when to apply them is the most important aspect of rules.
In this case, unit tests are a very reasonable place to "repeat yourself", so you don't have to figure out what it's actually doing. Seeing the code all in place makes life easier.
In this case, unit tests are a very reasonable place to "repeat yourself", so you don't have to figure out what it's actually doing. Seeing the code all in place makes life easier.