Test-driven development in Swift in iOS Swift

Introduction

Test-driven development helps you write code that works well by writing tests first. It makes your app more reliable and easier to fix.

When you want to make sure your app features work correctly before building them.

When you want to avoid bugs by checking your code step-by-step.

When you want to improve your coding skills by thinking about how your code should behave.

When you want to safely change or add new features without breaking existing ones.

Syntax

iOS Swift

func testExample() {
  // 1. Write a failing test
  XCTAssertEqual(add(2, 3), 5)
}

func add(_ a: Int, _ b: Int) -> Int {
  // 2. Write code to pass the test
  return a + b
}

// 3. Run tests and refactor if needed

Tests are written inside functions starting with test.

Use XCTAssert functions to check if your code works as expected.

Examples

This test checks if the sum function adds two numbers correctly.

iOS Swift

func testSum() {
  XCTAssertEqual(sum(1, 2), 3)
}

func sum(_ x: Int, _ y: Int) -> Int {
  return x + y
}

This test checks if the isEven function correctly identifies even numbers.

iOS Swift

func testIsEven() {
  XCTAssertTrue(isEven(4))
  XCTAssertFalse(isEven(5))
}

func isEven(_ number: Int) -> Bool {
  return number % 2 == 0
}

Sample App

This is a simple test class that checks if the add function returns the correct sum of two numbers.

When you run this test, it will pass if the sum is correct.

iOS Swift

import XCTest

class CalculatorTests: XCTestCase {
  func testAdd() {
    XCTAssertEqual(add(10, 5), 15)
  }
}

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

Important Notes

Write the test first, then write just enough code to pass it.

Run tests often to catch mistakes early.

Use descriptive test names to know what each test checks.

Summary

Test-driven development means writing tests before code.

Tests help you catch bugs early and keep your app working well.

Use XCTest in Swift to write and run your tests.