While I tend to agree, the Go toolchain authors are very specific: it doesn’t count as unit test coverage when the code and the test are in different packages.

While I tend to agree, the Go toolchain authors are very specific: it doesn’t count as unit test coverage when the code and the test are in different packages. And our management has no interest in breaking with them on this. You are free to write tests that compose packages, and I’ll do it for my own sanity and confidence. But that’s in addition to, not instead of, the minimum “not horrifically irresponsible engineering” standard of universal, exhaustive, very detail oriented mock driven unit tests within all packages.