It was noted earlier that the real purpose of unit testing code is about ensuring that code behaves in a predictable fashion across all possible execution cases. In a very real way, it is also about establishing a measure of trust in a code base. In that context, there is a line that has to be drawn with respect to where that trust can simply be taken as a given. For example, the various unit tests in this iteration have focused on ensuring that the code created for data persistence gets everything that is necessary to and from the database engine. It has not been concerned with whether the library to connect to the database engine is trustworthy; for our purposes, we assume that it is, at least until we encounter a test failure that cannot be explained in any other way.
Unit tests provide that trust for others who might consume our code – knowing...