Bridging Discrete and Continuous Logic in Automated Reasoning Systems https://chriskohlhepp.wordpress.com/the-reasoned-lisper/ (has some incredible examples)
miniblog.
Related Posts
I've worked on many projects where tests are have discrete levels, usually something like unit test, integration test, end-to-end test.
I've also seen elaborate arguments over what counts as a unit, especially in heavily OO codebases.