Test-driven development in Swift in iOS Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the main purpose of writing tests before code in TDD?

In Test-driven development (TDD), why do developers write tests before writing the actual code?

A To avoid writing any production code

B To make the app run faster

C To delay coding until all tests are ready

D To define the expected behavior and guide the implementation

💡 Hint

Think about how tests help shape the code you write.

In TDD, writing tests first helps clarify what the code should do, guiding development and ensuring correctness.

❓ ui_behavior

intermediate

What happens when a failing test is run in Xcode during TDD?

You write a test for a new feature in Swift and run it in Xcode, but the feature code is not implemented yet. What will you see?

A The test fails, showing a red indicator in the test navigator

B The test passes automatically

C The app UI updates to show the feature

D Xcode crashes

💡 Hint

Think about what happens when code does not meet test expectations.

A failing test shows a red mark in Xcode, indicating the feature is not yet implemented or does not behave as expected.

❓ lifecycle

advanced

What is the correct TDD cycle order?

Arrange the steps of the Test-driven development cycle in the correct order.

A 2,1,3,4

B 1,2,3,4

C 1,3,2,4

D 3,1,2,4

💡 Hint

Remember the mantra: Red, Green, Refactor.

TDD follows the cycle: write a failing test (red), write code to pass it (green), then refactor cleanly.

📝 Syntax

advanced

What is the output of this Swift test code snippet?

Consider this Swift test function: func testSum() { let result = sum(2, 3) XCTAssertEqual(result, 6) } Assuming sum adds two numbers, what will happen when this test runs?

iOS Swift

func sum(_ a: Int, _ b: Int) -> Int {
  return a + b
}

A The test is skipped automatically

B The test passes successfully

C The test fails because 2 + 3 is 5, not 6

D The test causes a runtime error

💡 Hint

Check the expected value in XCTAssertEqual.

The sum function returns 5, but the test expects 6, so the test fails.

🔧 Debug

expert

Why does this Swift test crash with 'fatal error: unexpectedly found nil while unwrapping an Optional'?

Given this test code: func testUserName() { let user: User? = nil XCTAssertEqual(user!.name, "Alice") } Why does this test crash instead of failing?

A Because user is nil and force-unwrapping it causes a runtime crash

B Because XCTAssertEqual cannot compare Optional values

C Because the test function is missing @testable import

D Because the name property is not defined in User

💡 Hint

Focus on the exclamation mark after user.

Force-unwrapping a nil Optional causes a runtime crash, not a test failure.