WorkingWithLegacyCode.swift

import UIKit
import PlaygroundSupport
import XCTest

struct Person {
  let firstName: String
  let lastName: String
  let address: String
}

struct ViewModel {
  var person: Person
  
  var nameAndAddress: String {
    return "\(person.firstName) \(person.lastName), \(person.address)"
  }

  init() {
    person = Person(firstName: "John",
                    lastName: "Appleseed",
                    address: "1 Infinite Loop, Cupertino, CA")
  }
}

let label = UILabel()
label.text = ViewModel().nameAndAddress
label.backgroundColor = UIColor.white
label.sizeToFit()

PlaygroundPage.current.liveView = label

class PersonTest: XCTestCase {
  override func setUp() {
    super.setUp()
  }
  
  override func tearDown() {
    super.tearDown()
  }
  
  func testResultOfNameAndAddressFunc() {
    XCTAssertEqual(ViewModel().nameAndAddress,
                   "John Appleseed, 1 Infinite Loop, Cupertino, CA")
  }
}

class PlaygroundTestObserver : NSObject, XCTestObservation {
  @objc func testCase(_ testCase: XCTestCase, didFailWithDescription description: String, inFile filePath: String?, atLine lineNumber: UInt) {
    print("Test failed on line \(lineNumber): \(testCase.name!), \(description)")
  }
}

let observer = PlaygroundTestObserver()
let center = XCTestObservationCenter.shared()
center.addTestObserver(observer)

struct TestRunner {
  
  func runTests(testClass:AnyClass) {
    print("Running test suite \(testClass)")
    let tests = testClass as! XCTestCase.Type
    let testSuite = tests.defaultTestSuite()
    testSuite.run()
    let run = testSuite.testRun as! XCTestSuiteRun
    
    print("Ran \(run.executionCount) tests in \(run.testDuration)s with \(run.totalFailureCount) failures")
  }
}

TestRunner().runTests(testClass: PersonTest.self)