I don’t want to take too much of a tangent, but in scientific studies, you are trying to understand some phenomena, and isolating variables can help with very complex things. A test is typically not that complex. Another example is the use of animals in testing medicine, it can help but it obviously would be much better to test directly on humans but we don’t for good reason.

Your position is reasonable and I do think isolation can be beneficial, but I still wouldn’t use mocking to do it.

>Smaller, more focused, cleaner tests are better in my opinion.

Cleaner is subjective. I can write “small” and “focused” functional tests that are also quick to run.

I am of the opinion that functional tests provide more value. They are testing more of the actual code than an approximation, which in turn gives a better indicator that it works. Functional tests are less likely to change unless the input/output changes.

Now let’s say you mock something in your function. Let’s say you make a change to that but the input and output are the exact same. Now you have to update your test.