Testing interview questions

Why unit tests

A teammate says they'd rather build one more feature than spend the time writing tests. How would you make the case for unit tests?

#unit-test #xctest #why-test #regression

XCTest discovery rules

Which conditions does a method need before XCTest recognizes and runs it as a test? Select all that apply.

#xctest #xctestcase #test-discovery

Test types and the pyramid

What's the difference between unit tests, integration tests, and UI tests?

#unit-test #integration-test #ui-test #test-pyramid

Telling test doubles apart

"I want to replace the analytics event sender and check in the test which events the view model sent, with which arguments, and how many times." Which test dou…

#test-double #spy #stub #mock

@testable import

When the test target does @testable import MyApp, which declarations become accessible?

#testable #access-control #test-target

TestingShort answerIntroPandorainterview report

Testing a playlist view model

A music app's playlist ViewModel takes a track list from a Repository and produces loading, success, and error states. How would you test those state transitio…

#unit-test #fake #viewmodel #state

Arrange-Act-Assert

Why do you split test code into Arrange-Act-Assert (Given-When-Then)?

#aaa #given-when-then #tdd #red-green-refactor

Test doubles

What is a test double?

#test-double #mock #stub #fake

Testing an API-backed screen

This screen leans heavily on an API response. How would you change the code so you can test the screen, view model included, without a server request?

#view-model #dependency-injection #stub #mvvm

Testing private methods

A private method inside a custom view holds complicated calculation logic and you want to test it. How would you test that private method, or should you leave …

#private #testable #encapsulation #custom-view

Testing async code

How do you test an async/await API in a unit test?

#async #xctestexpectation #async-await #swift-testing

XCTest lifecycle

In the XCTestCase below, which order are the calls made in when testA and testB run? …

#xctest #setup #teardown #lifecycle

Code coverage

Which statements about code coverage are correct? Select all that apply.

#coverage #xcode #metrics

Testing a view model

If you were testing load() on the view model below, which cases would you verify? …

#mvvm #view-model #observation #state

Swift Testing macros

Which statements about Swift Testing's #expect and #require are correct? Select all that apply.

#swift-testing #expect #require #macros

TestingShort answerBasicsX (Twitter)

Tests in a take-home

You got a take-home for a minimal iOS app with basic unit tests, and the brief says to finish in three to five hours. With time that tight, where would you put…

#take-home #unit-test #prioritization #architecture

TestingShort answerBasicsHeadspace

Tests in the workflow

This is a written question on a take-home: "how do you integrate tests into your development workflow?" Walk me through when and how tests run, from the moment…

#workflow #ci #pull-request #test-plan

TestingMultiple choiceBasicsApple

Testing a data structure

On CoderPad you're asked to implement a MaxStack where push, pop, top, and max are all O(1), built on a Swift protocol, and verify it with XCTest. Which are ap…

#xctest #test-design #edge-case #coderpad

TestingShort answerBasicsDeliveroo

Reviewing an iOS PR

A take-home asks you to review an existing PR and leave comments. When you review an iOS PR, what do you look at and in what order?

#code-review #pull-request #quality #take-home

TestingShort answerBasics토스interview report

Writing testable code

The question asks about your experience writing code with unit tests in mind and the philosophy you took from it. Give me the principles you hold to as concret…

#testability #dependency-injection #pure-function #design

TestingMultiple choiceBasics카카오뱅크interview report

Quick and Nimble

Your team's codebase uses Quick and Nimble. Which statements about the two libraries are correct? Select all that apply.

#quick #nimble #bdd #xctest

TestingShort answerBasicsBarclaysinterview report

Reading coverage

An iOS payment app has 90% line coverage, yet payment failure handling regresses every release. What does that 90% guarantee, and what does it fail to guarante…

#testing #coverage #risk #unit-test

TestingShort answerBasics요기요interview report

Trustworthy tests on CI

In a delivery app's iOS project the unit tests and UI tests pass locally but fail now and then only on CI. How would you cut down these flaky tests?

#ci #flaky-test #fixture #test-plan

TestingShort answerBasics마이리얼트립interview report

Scope of UI tests

A travel booking app's search screen UI tests call every API against the real server, so they're slow and break often. How would you split what stays a UI test…

#ui-test #stub #launch-arguments #testing-pyramid

TestingShort answerBasics클래스101interview report

The first TDD test

You're adding coupon discount pricing rules to an online course app with TDD. In the red-green-refactor cycle, which example would you pick as the first test?

#tdd #red-green-refactor #unit-test #refactoring

TestingShort answerBasicsSOOPinterview report

Testing an async stream

A live streaming app's chat ViewModel subscribes to incoming messages as an AsyncSequence and appends them to a list. How would you control that message stream…

#asyncstream #testing #cancellation #realtime

TestingShort answerBasics강남언니interview report

Regression tests in review

A PR fixing a bug in a beauty appointment app got a review comment saying there's no reproduction test. The reviewer has already read the code and could approv…

#code-review #regression #behavior #testing

TestingShort answerBasics번개장터interview report

Layers of test automation

You're adding automated tests to the listing feature of a secondhand marketplace app for the first time. What would you put on each of the three layers: unit t…

#test-pyramid #ci #automation #quality

Mocking the network

You want to test a network layer that uses URLSession directly, with no real server. Can you give me at least two ways to do it?

#urlsession #urlprotocol #mock #network

Replacing UI tests

You have dozens of UI tests that are slow and break often. How would you restructure the code and the tests to replace most of them with unit tests?

#ui-test #unit-test #presentation-logic #snapshot

Flaky tests

Which of the following cause flaky tests that fail only sometimes on CI? Select all that apply.

#flaky #determinism #shared-state #test-isolation

Testing Core Data and SwiftData

How do you set up unit tests for a store layer that depends on Core Data (or SwiftData) so that nothing is left on disk?

#core-data #swiftdata #in-memory #persistence-test

Swift Testing against XCTest

How is Swift Testing different from XCTest?

#swift-testing #xctest #migration #macros

Snapshot testing

You want to introduce snapshot testing to your team. What problem does snapshot testing solve?

#snapshot-test #visual-regression #swift-snapshot-testing #ci

Stabilizing UI tests

A login flow test written in XCUITest fails about 30% of the time on CI. What would you change on the app side to stabilize it?

#xcuitest #accessibility-identifier #launch-arguments #flaky

Testing time-dependent code

The "retry after three seconds" logic uses Task.sleep(for: .seconds(3)), so the test really waits three seconds each time. Which are correct approaches for mak…

#clock #time #task-sleep #determinism

TestingShort answerAdvancedGojek

TDD on an existing project

This one comes up onsite: "how does your team use tests today, and how would you follow TDD on a real project?" Answer it around a realistic way to bring TDD i…

#tdd #legacy #coverage #ui-test

TestingShort answerAdvancedWalmart

Unit testing around a singleton

An app calls AuthManager.shared directly all over the code. How would you unit test the code that depends on this singleton? …

#singleton #dependency-injection #test-isolation #protocol

TestingShort answerAdvancedDiscord

Architecture that invites tests

One item the architecture round scores is "can you add unit tests without a big refactor". Which design decisions satisfy that condition, with an example?

#architecture #testability #dependency-injection #design-round

TestingShort answerAdvancedCRED

What's worth testing

You just built a product list screen in a live coding round: view model, network, price formatting, and a favorite toggle. The interviewer asks, "on this scree…

#test-strategy #what-to-test #cost-benefit #priority

TestingMultiple choiceAdvancedFlipkart

URLProtocol-based mocking

To test the network layer you've decided to intercept responses with a URLProtocol subclass. Which statements are correct? Select all that apply. …

#urlprotocol #mocking #urlsession #network-test

TestingShort answerAdvanced센드버드interview report

Testing an SDK

Say you're building a chat SDK that ships inside other companies' apps rather than an app of your own. From a testing point of view, what changes compared with…

#sdk #integration-test #contract-test #backward-compatibility

Swift Testing execution model

In a suite written with Swift Testing, several tests write to and read from the same file path and fail intermittently. What's the most fundamental fix?

#swift-testing #parallel #serialized #shared-state

Testing concurrent code

How do you reproduce or detect a data race in concurrent code that uses actors and Tasks?

#actor #sendable #data-race #thread-sanitizer

Test strategy at scale

An app with 40 modules and 8,000 tests takes 40 minutes of CI tests. How would you change the test structure and the run strategy to get each PR under 10 minut…

#test-plan #modularization #ci #parallel

XCTestCase instance lifecycle

Which are problems with the test class below? Select all that apply. …

#xctest #lifecycle #memory #setup