Now that we know how to have working test suites for both our code and our documentation, the quality of those test suites fully depends on our capability to design and write good tests.
There is, by the way, one rule in software testing that can help us design good tests, and this is that errors usually hide in corner cases and limit values. If we have a function that performs division between two numbers, the bugs are probably going to be brought to the surface when zero, the maximum integer value, or negative numbers are passed to the function as arguments. Rarely will we see errors for most common values, such as 2, 3, 4, or 5. That's because developers usually tend to design their code with those common values in mind. The design that comes more naturally is usually the one that works for the most obvious cases, and corner cases rarely come to mind in the first instance.
Property-based testing comes in handy when easily generating tests that verify those...