This document tracks layer-wide conventions for Peridot code.
Test-only utils (but not the tests themselves) related to a given library should be placed under the directory of the library itself, in a subdirectory called testing (and not test).
The test-only symbols should be declared in the same namespace as the library the test helpers are related to (and not in a test or testing subnamespace).
The build targets containing test-only utils should be marked as such using the GN testonly = true annotation.
