The Query Integration team has recently started writing end-to-end tests for the Extensions API, which is only available on Linux machines, and we'll continue to increase our end-to-end testing. We've been using the isLinux() util function from os_helpers.js to quit() tests if being run on non-Linux but it'd be much more efficient to skip those tests entirely. We can use "incompatible_with_macos" and "incompatible_with_windows_tls" to do a best attempt, but it'd be better to have a correct "linux_only" tag or alike.