Test-driven development in Swift in iOS Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a test case class in Swift.

iOS Swift

import XCTest

class [1]: XCTestCase {
}

Drag options to blanks, or click blank then click option'

AUnitTest

BMyTestCase

CTestClass

DTestCase

Attempts:

3 left

💡 Hint

Common Mistakes

Using a class name that does not inherit from XCTestCase

Forgetting to import XCTest

The test case class must inherit from XCTestCase. Naming it MyTestCase is a common convention.

2fill in blank

medium

Complete the code to write a test method that checks if 2 + 2 equals 4.

iOS Swift

func testAddition() {
    XCTAssertEqual([1], 4)
}

Drag options to blanks, or click blank then click option'

A2 + 2

B1 + 2

C2 + 3

D3 + 3

Attempts:

3 left

💡 Hint

Common Mistakes

Using an expression that does not equal 4

Forgetting to use XCTAssertEqual

The test checks if 2 + 2 equals 4. This is a simple assertion example.

3fill in blank

hard

Fix the error in the test method declaration to make it a valid test method in Swift.

iOS Swift

func [1]() {
    XCTAssertTrue(true)
}

Drag options to blanks, or click blank then click option'

ATestMethod

BverifyMethod

CcheckMethod

DtestMethod

Attempts:

3 left

💡 Hint

Common Mistakes

Starting method name with uppercase 'Test'

Using names that do not start with 'test'

Test methods must start with test in lowercase to be recognized by XCTest.

4fill in blank

hard

Fill both blanks to create a test that fails if the value is not nil.

iOS Swift

func testValueIsNil() {
    let value: String? = nil
    XCTAssert[1](value [2] nil)
}

Drag options to blanks, or click blank then click option'

ATrue

B==

C!=

DEqual

Attempts:

3 left

💡 Hint

Common Mistakes

Using XCTAssertEqual instead of XCTAssertTrue

Using '!=' instead of '==' for nil comparison

XCTAssertTrue checks if a value is nil. The comparison uses == nil to confirm the value is nil.

5fill in blank

hard

Fill all three blanks to write a test that verifies a function returns true for positive numbers.

iOS Swift

func testIsPositive() {
    let number = 5
    let result = isPositive([1])
    XCTAssert[2](result == [3])
}

Drag options to blanks, or click blank then click option'

Anumber

BTrue

Ctrue

Dnumber + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Passing an incorrect argument to the function

Using XCTAssertFalse instead of XCTAssertTrue

Using uppercase 'True' instead of lowercase 'true'

The function isPositive is called with number. The test asserts the result is true using XCTAssertTrue.

Practice

1. What is the main idea behind Test-driven development (TDD) in Swift?

easy

A. Write tests before writing the actual code

B. Write code first, then write tests later

C. Write tests only after the app is complete

D. Skip tests and focus on UI design

Solution

1. Step 1: Understand TDD concept

   TDD means you write tests before you write the code that makes those tests pass.

2. Step 2: Compare options with TDD definition

   Only Write tests before writing the actual code correctly states that tests come before code in TDD.

3. Final Answer:

   Write tests before writing the actual code -> Option A

4. Quick Check:

   TDD = Write tests first [OK]

Hint: Remember: Tests come first in TDD [OK]

Common Mistakes:

• Thinking tests are written after code
• Believing tests are optional
• Confusing TDD with UI design

2. Which of the following is the correct way to import the testing framework in a Swift test file?

easy

A. import XCTest

B. import SwiftTest

C. import TestKit

D. import Testing

Solution

1. Step 1: Identify the official Swift testing framework

   The official framework for testing in Swift is called XCTest.

2. Step 2: Match the import statement

   Only import XCTest is correct to use XCTest in your test files.

3. Final Answer:

   import XCTest -> Option A

4. Quick Check:

   Use XCTest for Swift tests [OK]

Hint: Always import XCTest for Swift tests [OK]

Common Mistakes:

• Using incorrect or non-existent import names
• Forgetting to import XCTest
• Confusing XCTest with other frameworks

3. Given the following Swift test code, what will be the test result?

func testSum() {
  let result = sum(2, 3)
  XCTAssertEqual(result, 5)
}

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

medium

A. Test fails because sum(2, 3) equals 6

B. Test passes but result is 6

C. Test fails due to syntax error

D. Test passes because sum(2, 3) equals 5

Solution

1. Step 1: Analyze the sum function

   The function adds two integers and returns their sum. sum(2, 3) returns 5.

2. Step 2: Check the test assertion

   The test asserts that result equals 5, which is true, so the test passes.

3. Final Answer:

   Test passes because sum(2, 3) equals 5 -> Option D

4. Quick Check:

   sum(2,3) == 5 passes test [OK]

Hint: Check function output matches XCTAssertEqual value [OK]

Common Mistakes:

• Assuming sum returns wrong value
• Confusing test failure with syntax error
• Ignoring the actual return value

4. Identify the error in this Swift test code snippet:

func testIsEven() {
  let number = 4
  XCTAssertTrue(isEven(number))
}

func isEven(_ n: Int) -> Bool {
  return n % 2 == 1
}

medium

A. XCTAssertTrue is used incorrectly; should be XCTAssertFalse

B. The isEven function returns true for odd numbers, causing test failure

C. The test function name is invalid

D. Missing import XCTest statement

Solution

1. Step 1: Check the isEven function logic

   It returns true if n % 2 == 1, which means odd numbers, not even.

2. Step 2: Understand test expectation

   The test expects isEven(4) to be true, but 4 is even, so the function logic is wrong and test fails.

3. Final Answer:

   The isEven function returns true for odd numbers, causing test failure -> Option B

4. Quick Check:

   Wrong modulo logic causes test fail [OK]

Hint: Check function logic matches test expectation [OK]

Common Mistakes:

• Mixing odd/even logic in modulo
• Misusing XCTAssertTrue vs XCTAssertFalse
• Ignoring function implementation errors

5. You want to use TDD to create a function that filters out negative numbers from an array. Which sequence of steps follows TDD best?

hard

A. Write tests only for positive numbers, ignore negatives

B. Write the filtering function first, then write tests after it works

C. Write a failing test for filtering negatives, write code to pass test, refactor code

D. Write code and tests simultaneously without order

Solution

1. Step 1: Understand TDD workflow

   TDD requires writing a failing test first that defines desired behavior.

2. Step 2: Follow TDD steps for filtering negatives

   Write a test that expects negatives filtered out, then write code to pass it, then improve code.

3. Final Answer:

   Write a failing test for filtering negatives, write code to pass test, refactor code -> Option C

4. Quick Check:

   TDD = Test first, code second, refactor [OK]

Hint: Always write failing test before code in TDD [OK]

Common Mistakes:

• Writing code before tests
• Ignoring refactoring step
• Writing incomplete tests