XCTest doing absolutely nothing? Lack of documentation driving you insane? Avoiding a DTS ticket? Here's a Swift class that forcibly bootstraps XCTest when running inside of a test host and XCTest is not starting itself.

why.md

If you're in an atypical codesigning environment you may run into an issue where xctest fails to bootstrap when running inside of a test host. I have no clue why, nor do I care. I would rather have my tests work with my private entitlements with zero friction. This helper class will do what XCTest normally does when running inside of a test host, which is:

• Loads your xctest bundle
• Calls XCTestMain

XCTHarness.swift

public class XCTHarness {
    private typealias XCTestMainType = @convention(c) (_ something: AnyObject?) -> ()

    private static func dlsymcast<T>(_ handle: UnsafeMutableRawPointer!, _ symbol: UnsafePointer<CChar>) -> T! {
        dlsym(handle, symbol).map {
            if T.self is AnyObject.Type {
                return $0 as! T
            } else {
                return unsafeBitCast($0, to: T.self)
            }
        }
    }
    
    // sanity check for troubleshooting, if this is missing we are most likely being invoked manually and whoever invoked us forgot something
    private static let isTestSession = ProcessInfo.processInfo.environment.keys.contains("XCTestSessionIdentifier")
    
    // /Applications/Xcode-13.3.1.app/Contents/Developer/../SharedFrameworks/
    private static let libraryPath = ProcessInfo.processInfo.environment["LD_LIBRARY_PATH"].map(URL.init(fileURLWithPath:))

    // /Applications/Xcode-13.3.1.app/Contents/Developer/../SharedFrameworks/XCTestCore.framework/Versions/Current/XCTestCore
    private static let XCTestCorePath = libraryPath?.appendingPathComponent("XCTestCore.framework/Versions/Current/XCTestCore").path
    private static let XCTestCore = XCTestCorePath.flatMap { dlopen($0, RTLD_LAZY) }
    
    // /Applications/Xcode-13.3.1.app/Contents/Developer/../SharedFrameworks/XCTest.framework/Versions/Current/XCTest
    private static let XCTestPath = libraryPath?.appendingPathComponent("XCTest.framework/Versions/Current/XCTest").path
    private static let XCTest = XCTestPath.flatMap { dlopen($0, RTLD_NOW) }
    
    // dlsym(XCTestCore.framework, _XCTestMain)
    private static let XCTestMain = XCTestCore.flatMap { dlsymcast($0, "_XCTestMain") as XCTestMainType? }
    
    // relative path from our bundle path to the .xctest containing the tests we are going to run
    private static let XCTestBundlePath = ProcessInfo.processInfo.environment["XCTestBundlePath"]
    private static let XCTestBundle = XCTestBundlePath.flatMap { Bundle(url: Bundle.main.bundleURL.appendingPathComponent($0)) }
    
    public static func forceStartTestSession() {
        if !XCTHarness.isTestSession {
            print("Missing XCTestSessionIdentifier, things might not work. I don't think I'm where I'm supposed to be.")
        }
        guard let _ = XCTHarness.XCTest else {
            guard let XCTestPath = XCTHarness.XCTestPath else {
                fatalError("Missing LD_LIBRARY_PATH! Xcode inserts this automatically when running a test host, are you Xcode? What's up buddy?")
            }
            fatalError("Couldn't find XCTest.framework, expected it at \(XCTestPath)")
        }
        guard let XCTestBundle = XCTHarness.XCTestBundle else {
            guard let XCTestBundlePath = XCTHarness.XCTestBundlePath else {
                fatalError("Missing XCTestBundlePath! Xcode inserts this automatically when running a test host, are you Xcode? What's up buddy?")
            }
            fatalError("Couldn't find XCTestBundle, expected it at \(XCTestBundlePath)")
        }
        guard XCTestBundle.load() else {
            fatalError("Can't load xctest bundle at \(XCTHarness.XCTestBundlePath!)")
        }
        guard let XCTestMain = XCTHarness.XCTestMain else {
            fatalError("Can't find _XCTestMain inside \(XCTestCorePath!), I fear DVT has bamboozled us.")
        }
        XCTestMain(nil)
    }
}