Thread by @joemasilotti

XCTest tips and tricks that can level up your Swift testing.

🧵👇

1. Use XCTUnwrap instead of force wrapping optionals

Force unwrapping a nil will cause the test suite to completely crash, meaning no output or reporting. XCTUnwrap provides a nice failure message and fails the test.

2. Set continueAfterFailure to false

If you have multiple assertions in a test they might increase in specificity. The first asserts the size of the array and the second assets the first element. You don't want to run the second if the first fails, it's just noise.

3. Use KVO observing asynchronous expectations

Use XCTKVOExpectation to assert KVO-compliant properties on your subject under test.

let expectation = keyValueObservingExpectation(for: subject, keyPath: "property", expectedValue: value)
wait(for: [expectation], timeout: 1)

4. Assert types with XCTAssert and "is"

This technique is helpful when you only care about the type and not a particular instance.

XCTAssert(controller.presentedViewController is CustomViewController)

5. Keep XCTAssertEqual parameter order consistent

The documentation doesn't indicate if the expected or actual value should be first. Pick one and stick with it to make it obvious which is which for any test. (Personally, I put the actual value first.)

6. Extract helpers judiciously

If I need 3 or more lines of code to "do something" I extract it to a helper. This includes test setup, the action, and the assertion(s). Define the function with #filepath and #line to pass along test failures to the caller.

If you made it this far you might also enjoy reading Masilotti.com, where I blog about testing in Swift.

What other XCTest tips have you picked up? Reply here I'll add them to this thread!

7. Add test extensions to models to make your code easier to understand by reducing noise via @lightsprint09

struct User {
let firstName: String
let lastName: String
}

extension User {
static func build(firstName: String = "Joe", lastName: String = "Masilotti") { ... }
}

8. Conform to Equatable to combine assertions via @lightsprint09

let user = controller.user
XCTAssertEqual(user, User(name: "Joe"))

extension User: Equatable {
func ==(_ lhs: User, _ rhs: User) -> Bool {
lhs.name == rhs.name
}
}

9. Always make your tests throw via @forceunwrap

func test_somethingHappens() throws { }

Adding throws to the end of the test captures any raised exceptions and let's you use "try" without ? or ! throughout the test.

10. Use protocols for the APIs you want to test. Mock extensively via @dasdom

Way too much for a tweet, so here’s an entire blog post! masilotti.com/better-swift-u…