NEW: Nominations are now open for the 2019 Swift Community Awards! >>

How to check and unwrap optionals in tests using XCTUnwrap()

Swift version: 5.1

Paul Hudson    @twostraws   

When writing tests, it’s common to want to unwrap an optional before checking it for a particular value. XCTUnwrap() does exactly that for us: it attempts to unwrap the optional, but will throw an error (and thus fail the test) if the optional is nil.

For example, if you have a User struct with a getAuthenticationToken() method that returns an optional string, you can use XCTUnwrap() like this:

func testTokenGenerationSucceeds() throws {
    let user = User()
    let token = try XCTUnwrap(user.getAuthenticationToken())
    XCTAssertEqual(token.count, 40)
}

That test is marked with throws, which allows us to call XCTUnwrap() and propagate any errors if it finds our optional is empty.

This approach is cleaner than what we might have written previously:

func testTokenGenerationSucceeds2() {
    let user = User()
    if let token = user.getAuthenticationToken() {
        XCTAssertEqual(token.count, 40)
    } else {
        XCTFail("Failed to generate valid token.")
    }
}

It’s worth adding that in trivial cases such as this one, it’s possible to compare optionals with non-optionals in less code, like this:

func testTokenGenerationSucceeds3() throws {
    let user = User()
    XCTAssertEqual(user.getAuthenticationToken()?.count, 40)
}

However, things aren’t so straightforward when you need to work with optional chaining in a longer test – that’s really where XCTUnwrap() will come into its own.

LEARN SWIFTUI FOR FREE I have a massive, free SwiftUI video collection on YouTube teaching you how to build complete apps with SwiftUI – check it out!

Available from iOS 13.0

Similar solutions…

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.

MASTER SWIFT NOW
Buy Testing Swift Buy Practical iOS 12 Buy Pro Swift Buy Swift Design Patterns Buy Swift Coding Challenges Buy Server-Side Swift (Vapor Edition) Buy Server-Side Swift (Kitura Edition) Buy Hacking with macOS Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with Swift Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Beyond Code

Was this page useful? Let us know!

Average rating: 5.0/5