iOS Unit-Test Tips & Tricks

After few years working with iOS Unit-Test I conducted some tips & tricks to help to write a reliable & effectively unit-test.

Time-out should be 0.1 rather than 1 or 3

waitForExpectations(timeout: 0.1) { _ in }

wait(for: [expectation], timeout: 0.1)

• Apple does provide this in XCTest to sever all kind of Testing: Unit-Test, Integration Test, UITest
• Write a unit-test that depend on the timing that not a good test, will your test failed if the time-out is zero? If it failed means you’re not doing DI & Mocking well.
• It not make your test-case passes faters, but if it’s failed, do make failed faster. This will help your CI/CD reduce a lot of time!
• At the first glance to see a long time-out, it will make you feeling that something underneath is realy complicated.
• 0.1 or 3 does not matter, mocking matters!
• I have some more details on it https://geek-is-stupid.github.io/2020-03-18-Unit-Test-asynchronous-timeout-0-1-seconds/

Not to stubbing in setUp method if not needed

• Redundant code, some test case don’t need to use that stub, so you’re adding a un-needed implementation.
• It won’t protect your code! Imagine that in the future your teammate make another call to existing dependency, your test won’t failed, because all is stubbed in setUp method.
• When the test case is removed, will you/your teammate remember to remove that stub?
• If you think it’s reusable code, then you can separate to a method, and calling that method from your test method.
• Don’t be lazy! 💪

Always using setUp & tearDown

• In my experiences with Unit-Test on Objective-C & Swift, using OCMock and Cuckoo, we run into a problem that when the amount of test cases reach almost 10k, your Test Target gonna be “laggy”, some test classes are leaked 😱
• To avoid the problem above, we do add testSetUp & tearDown to clean up the memory were allocated during testing, all mocks & sut should be set to nil.

var sut: YourClass!
var yourMock: MockYour!
    
override func setUp() {
    super.setUp()
    sut = YourClass()
    yourMock = YourMock()
    sut.yourMock = yourMock
}

override func tearDown() {
    sut = nil
    yourMock = nil
    super.tearDown()
}
    
func testMethod() {...}

Dispose your RxSwift subscriptions

To be safe, to not making any leak, or release immediately your memory, please do dispose your subscription!

func testFetchPartnershipProgramDetailByCode() {
    // Given:
    let expected = expectation(description: #function)

    // When:
    let subscription = sut.fetch()
        .subscribe(onNext: { _ in
            expected.fulfill()
        })

    // Then:
    waitForExpectations(timeout: 0.1) { _ in
        subscription.dispose()
    }
}

Combine with BBD - Given - When - Then

• In my experiences that writing unit-tests take a lot of time, but when maintain someone unit-tests even take a lot of more time & effort
• If you and you team, set some rules to make sure the anyone can understand & maintainable

func testMethodName() {
	// Given:
	/// Stubbing, mocking, preparing data for test
	
	// When:
	sut.methodName()
	
	// Then:
	// Assertion places, verify
}

Handling Test Case Failure

• Settings executionTimeAllowance for limit number of minutes to run a test
• Turn continueAfterFailure to false to end execution of that method as soon as a failure occurs.

Understanding Setup and Teardown for Test Methods

https://developer.apple.com/documentation/xctest/xctestcase/understanding_setup_and_teardown_for_test_methods