How to unit test throwing functions in Swift?

Question

How to test wether a function in Swift 2.0 throws or not? How to assert that the correct ErrorType is thrown?

Answer 1

At least of Xcode 7.3 (maybe earlier) you could use built-in XCTAssertThrowsError():

XCTAssertThrowsError(try methodThatThrows())

If nothing is thrown during test you'll see something like this:

If you want to check if thrown error is of some concrete type, you could use errorHandler parameter of XCTAssertThrowsError():

enum Error: ErrorType {
    case SomeExpectedError
    case SomeUnexpectedError
}

func functionThatThrows() throws {
    throw Error.SomeExpectedError
}

XCTAssertThrowsError(try functionThatThrows(), "some message") { (error) in
    XCTAssertEqual(error as? Error, Error.SomeExpectedError)
}