Fix selection sort and add tests; fixes #414 (#418)

* Fix selection sort and add tests; fixes #414 
Co-authored-by: vinayak <itssvinayak@gmail.com>

Sorts/SelectionSort.js

@@ -8,12 +8,19 @@
  *from the unsorted subarray is picked and moved to the sorted subarray.
  */
 
-function selectionSort (items) {
-  var length = items.length
-  for (var i = 0; i < length - 1; i++) {
+const selectionSort = (list) => {
+  if (!Array.isArray(list)) {
+    throw new TypeError('Given input is not an array')
+  }
+  const items = [...list] // We don't want to modify the original array
+  const length = items.length
+  for (let i = 0; i < length - 1; i++) {
+    if (typeof items[i] !== 'number') {
+      throw new TypeError('One of the items in your array is not a number')
+    }
     // Number of passes
-    var min = i // min holds the current minimum number position for each pass; i holds the Initial min number
-    for (var j = i + 1; j < length; j++) { // Note that j = i + 1 as we only need to go through unsorted array
+    let min = i // min holds the current minimum number position for each pass; i holds the Initial min number
+    for (let j = i + 1; j < length; j++) { // Note that j = i + 1 as we only need to go through unsorted array
       if (items[j] < items[min]) { // Compare the numbers
         min = j // Change the current min number position if a smaller num is found
       }
@@ -21,16 +28,23 @@ function selectionSort (items) {
     if (min !== i) {
       // After each pass, if the current min num != initial min num, exchange the position.
       // Swap the numbers
-      [items[i], items[min]] = [items[min], [items[i]]]
+      [items[i], items[min]] = [items[min], items[i]]
     }
   }
+  return items
 }
 
-// Implementation of Selection Sort
+/* Implementation of Selection Sort
 
-var ar = [5, 6, 7, 8, 1, 2, 12, 14]
+(() => {
+  let array = [5, 6, 7, 8, 1, 2, 12, 14]
   // Array before Sort
-console.log(ar)
-selectionSort(ar)
+  console.log(array)
+  array = selectionSort(array)
   // Array after sort
-console.log(ar)
+  console.log(array)
+})()
+
+*/
+
+export { selectionSort }

Sorts/SelectionSort.test.js

@@ -0,0 +1,22 @@
+import { selectionSort } from './SelectionSort'
+
+describe('selectionSort', () => {
+  it('expects to return the array sorted in ascending order', () => {
+    var toSort = [5, 6, 7, 8, 1, 2, 12, 14]
+    const expected = [1, 2, 5, 6, 7, 8, 12, 14]
+
+    expect(selectionSort(toSort)).toEqual(expected)
+  })
+
+  it('expects to throw if it is not a valid array', () => {
+    expect(() => selectionSort('abc')).toThrow('Given input is not an array')
+    expect(() => selectionSort(123)).toThrow('Given input is not an array')
+    expect(() => selectionSort({})).toThrow('Given input is not an array')
+    expect(() => selectionSort(null)).toThrow('Given input is not an array')
+    expect(() => selectionSort()).toThrow('Given input is not an array')
+  })
+
+  it('expects to throw if one of the elements in the array is not a number', () => {
+    expect(() => selectionSort([1, 'x', 2])).toThrow('One of the items in your array is not a number')
+  })
+})