[nradov]

Except that it's tough to make performance and efficiency tests actually persist. The expected test results have to be keyed to the particular test environment and so those tests can't really be portable to other computers. And then every time you upgrade or change the test environment you have to modify the tests with different expected results.

The only way to make such tests really persist is to build in some kind of fixed known benchmark to evaluate baseline performance in the test environment, and then evaluate the software under test relative to that benchmark. This is a huge extra effort and hard to get right.