Add unit tests for documented examples of rotate functions

Author: mdznr

Tests/SwiftAlgorithmsTests/RotateTests.swift

@@ -13,6 +13,20 @@ import XCTest
 import Algorithms
 
 final class RotateTests: XCTestCase {
+  func testRotateSubrangeExample() {
+    var numbers = [10, 20, 30, 40, 50, 60, 70, 80]
+    let oldStart = numbers.rotate(subrange: 0..<4, toStartAt: 2)
+    XCTAssertEqual(numbers, [30, 40, 10, 20, 50, 60, 70, 80])
+    XCTAssertEqual(numbers[oldStart], 10)
+  }
+  
+  func testRotateExample() {
+    var numbers = [10, 20, 30, 40, 50, 60, 70, 80]
+    let oldStart = numbers.rotate(toStartAt: 3)
+    XCTAssertEqual(numbers, [40, 50, 60, 70, 80, 10, 20, 30])
+    XCTAssertEqual(numbers[oldStart], 10)
+  }
+  
   func testRotate() {
     for length in 0...15 {
       let a = Array(0..<length)