mr-v/AssertThrows

Assertions for unit testing throwing functions in Swift

AssertThrows

Custom assertions for unit testing throwing functions. Originally written for Swift 2. For more information see blog post.

Usage

Custom assertions enable following tests:

1. Throws error.
2. Throws specific ErrorType implementer.
3. Throws specific case of ErrorType implementer.*

Sample usage:

func test_AssertsThrowingAnyError() {
    let movie = Movie()
    AssertThrows(try movie.throwOnUnkown(.Unkown))
}

func test_AssertsThrowingSpecificType() {
    let movie = Movie()
    AssertThrows(TestError.self, try movie.throwOnUnkown(.Unkown))
}

func test_AssertThrows_ThrowingSpecificCaseOfType() {
    let movie = Movie()
    AssertThrows(TestError.IllegalArgument, try movie.throwOnUnkown(.Unkown))
}

There's one caveat - ErrorType conforming enumerations with associated data must also implement Equatable protocol to be verified with AssertThrows. Standard enums have it for free.

Custom assertions fix issues with vanilla XCTest tests that may have looked like this:

func test_throwOnUnkown_UnknownPassed_ThrowsAnyError() {
    do {
        try Movie().throwOnUnkown(.Unkown)
        XCTFail()
    } catch {
    }
}

func test_throwOnUnkown_UnknownPassed_ThrowsTestError() {
    do {
        try Movie().throwOnUnkown(.Unkown)
        XCTFail()
    } catch {
        guard let _ = error as? TestError else {
            return XCTFail()
        }
    }
}

func test_throwOnUnkown_UnknownPassed_ThrowsIllegalArgument() {
    do {
        try Movie().throwOnUnkown(.Unkown)
        XCTFail()
    } catch {
        guard let error = error as? TestError else {
            return XCTFail()
        }
        XCTAssertEqual(TestError.IllegalArgument, error)
    }
}

Installation

CocoaPods

In Podfile add AssertThrows to test target, e.g.

target 'AppTests' do
pod 'AssertThrows'
end

Carthage

Add to Cartfile:

github "mr-v/AssertThrows"

Drag the built .framework binary into your application’s test target.