Make Testing Easy
I took the time the other day to make it possible to write some very similar tests with one line, calling a generic testing function. I found that I wrote more tests, because it was so easy, and the individual tests were very easy to read and understand.
Fewer Assertions (per Test)
I spent [DELETED] time a day or so ago, trying to figure out how a test result could possibly be what it was. I expected something like Expected 28, Got 30, but it said Expected 19, Got 20. Impossible … until I realized there were two assertions in the test and it was the first one, which I was sure would work, that was failing. Single-assertion tests are easier to understand, and point to the error when they fail.