Paraphrasing the famous quote: There are only two hard problems in CS: naming things and cache expiration.

An issue I see with this is that there's a potential window when tests pass with bad data. For example, tests using a mock and the mock is periodically verified with a service call. The mock could become bad data, but won't be marked as bad until the next service call verification. Until that happens, the tests using the mock will all pass. It's not clear from the article how they address this.