Traditional testing wisdom eventually invokes the test pyramid, which is a guide to the proportion of tests to write along the isolation / integration spectrum. There’s an eternal debate about what the best proportion should be at each level, but interestingly it’s always presented with the assumption that test cases are hand-written. We should also think about test generation as a dimension, and if I were to draw a pyramid about it I’d place generated tests on the bottom and hand-written scenarios on top, i.e. most tests should be generated.
Source: Most Tests Should Be Generated, an article by Alex Weisberger.