example for an article

3.GuardBlackSheep.swift

extension XCTestCase {
    func g<T>(array: [T], at index: Int, file: StaticString = #file, line: UInt = #line) -> T {
        continueAfterFailure = false
        guard index < array.count else {
            XCTFail("index out of range", file: file, line: line)
            precondition(false)
        }
        return array[index]
    }
    
    func uw<T>(variable: T?, file: StaticString = #file, line: UInt = #line) -> T {
        continueAfterFailure = false
        guard let variable = variable else {
            XCTFail("unexpectedly found nil while unwrapping an Optional value", file: file, line: line)
            precondition(false)
        }
        return variable
    }
}