Get gets the value of a test hook. In production mode it always returns the zero value and
false, which hopefully the compiler will inline and remove the hook as dead code.
TestHooks should be used very sparingly, see comment on TestHooks.
TestHooks (in production mode) is an empty struct just so the build works.
See TestHooks in test_impl.go.
TestHooks are an inherently unclean way of writing tests. They require mixing test-only
concerns into production code. In general you should prefer other ways of writing tests
wherever possible, and only use TestHooks sparingly, as a last resort.