We don't, that's why we do review it. We also do things like communicate with teammates, have expectations of not wasting other people's time, and try to uphold standards and meet SLAs. Maybe people should worry about why their teams are so dysfunctional rather than how the code was produced
When I was in a test-driven development environment, one of our rules was that you had to see the test fail. You had to prove that it would actually test what you were trying to test.