Guava has staggering numbers of unit tests: as of July 2012, the guava-tests package includes over 286,000 individual test cases. Most of these are automatically generated, not written by hand, but Guava's test coverage is extremely thorough, especially for com.google.common.collect.
How they were generated? What techniques and technologies were used to design and generate them?
My first guess is they follow parametrized tests approach. The package com.google.common.collect.testing has a lot of classes with "Generator" in their names -- making it look like a framework for tests generation. The package com.google.common.collect.testing.features lists the features/constrains that a "collection" implementation (e.g., for a list, a set) should satisfy. So a test case parametrize what features a particular implementation should have.
My original question on Programmers SE got much attention from the community but no reasonable answer, so I'm trying to get it here. My motivation behind such a question is to learn more in general about techniques (parametrized tests, random tests, etc.) and technologies (code templates, etc.) used to automate test case generation.