Compiling Test Code with #if FASTLANE Using Swift

When creating screenshots with fastlane, there is support for checking at runtime within the app whether fastlane is being used by looking at a user default:

if UserDefaults.standard.bool(forKey: "FASTLANE_SNAPSHOT") {
    // runtime check that we are in snapshot mode
}

Unfortunately, that does not work from within the test code since the tests are run in a separate helper app!

In the test code, I would like to use something like the following such that I can test and tweak the code within Xcode before running fastlane on it:

#if FASTLANE
    snapshot("1_init", timeWaitingForIdle: 0)
#else
    let attach = XCTAttachment(screenshot: XCUIScreen.main.screenshot())
    attach.lifetime = .keepAlways
    add(attach)
#endif

One would think the FASTLANE_SNAPSHOT=YES build setting would be suitable for this task, but I have not found any way to detect it from within Swift, possibly because values like YES are not supported by the compiler.

This, however, seems to do the trick: Add this line to your Snapfile:

# Add a define for xcodebuild
xcargs "SWIFT_ACTIVE_COMPILATION_CONDITIONS=FASTLANE"