truncate by words swift 4

String.swift

//
//  String.swift
//  MyModule
//
//  Created by Shaun Hubbard on 10/9/17.
//  Copyright © 2017 MyCompany, LLC. All rights reserved.
//

import Foundation

extension String {
  func truncate(wordCount: Int, trailing: String = "...") -> String {
    let words = self.components(separatedBy: CharacterSet.whitespaces)
    if words.count > wordCount {
      return words[..<wordCount].joined(separator: " ") + trailing
    } else {
      return self
    }
  }
}

StringTests.swift

//
//  StringTests.swift
//  MyModuleTests
//
//  Created by Shaun Hubbard on 10/9/17.
//  Copyright © 2017 MyCompany, LLC. All rights reserved.
//

import XCTest
@testable import MyModule

class StringTests: XCTestCase {
  func testTruncateWhenToShortByWordCount() {
    let testString = "Don't Truncate me"

    XCTAssertEqual(testString.truncate(wordCount: 3), testString)
  }

  func testTruncateWithWordCount() {
    let testString = "Do by all means truncate me"

    XCTAssertEqual(testString.truncate(wordCount: 3), "Do by all...")
  }
}