Unit Test fatalError in Swift -

how implement unit test fatalerror code path in swift?

for example, i've following swift code

func divide(x: float, y: float) -> float {      guard y != 0 else {         fatalerror("zero division")     }      return x / y } 

i want unit test case when y = 0.

note, want use fatalerror not other assertion function.

the idea replace built-in fatalerror function own, replaced during unit test's execution, run unit test assertions in it.

however, tricky part fatalerror @noreturn, need override function never returns.

override fatalerror

in app target (don't add unit test target):

// overrides swift global `fatalerror` @noreturn func fatalerror(@autoclosure message: () -> string = "", file: staticstring = __file__, line: uint = __line__) {     fatalerrorutil.fatalerrorclosure(message(), file, line)     unreachable() }  /// `noreturn` function pauses forever @noreturn func unreachable() {     repeat {         nsrunloop.currentrunloop().run()     } while (true) }  /// utility functions can replace , restore `fatalerror` global function. struct fatalerrorutil {      // called custom implementation of `fatalerror`.     static var fatalerrorclosure: (string, staticstring, uint) -> () = defaultfatalerrorclosure      // backup of original swift `fatalerror`     private static let defaultfatalerrorclosure = { swift.fatalerror($0, file: $1, line: $2) }      /// replace `fatalerror` global function else.     static func replacefatalerror(closure: (string, staticstring, uint) -> ()) {         fatalerrorclosure = closure     }      /// restore `fatalerror` global function original swift implementation     static func restorefatalerror() {         fatalerrorclosure = defaultfatalerrorclosure     } } 

extension

add following extension unit test target:

extension xctestcase {     func expectfatalerror(expectedmessage: string, testcase: () -> void) {          // arrange         let expectation = expectationwithdescription("expectingfatalerror")         var assertionmessage: string? = nil          // override fatalerror. pause forever when fatalerror called.         fatalerrorutil.replacefatalerror { message, _, _ in             assertionmessage = message             expectation.fulfill()         }          // act, perform on separate thead because call fatalerror pauses forever         dispatch_async(dispatch_get_global_queue(qos_class_user_initiated, 0), testcase)          waitforexpectationswithtimeout(0.1) { _ in             // assert             xctassertequal(assertionmessage, expectedmessage)              // clean              fatalerrorutil.restorefatalerror()         }     } } 

testcase

class testcase: xctestcase {     func testexpectpreconditionfailure() {         expectfatalerror("boom!") {             dosomethingthatcallsfatalerror()         }     } } 

i got idea post unit testing assert , precondition: testing assertion in swift