input: Write a function to sort a list of numbers using the Insertion Sort algorithm. If the given list is empty, return an empty list.
  assert insertionSort([2, 4, 7, 3, 8, 6, 1])==[1, 2, 3, 4, 6, 7, 8]
  assert insertionSort([5, 3, 8, 6, 7, 2])==[2, 3, 5, 6, 7, 8]
  assert insertionSort([1, 2, 3, 4, 5])==[1, 2, 3, 4, 5]
  assert insertionSort([])==[]
  assert insertionSort([9, 8, 7, 6, 5, 4, 3, 2, 1])==[1, 2, 3, 4, 5, 6, 7, 8, 9]
output: def insertionSort(arr):
      if not arr:
          return []
      for i in range(1, len(arr)):
          key = arr[i]
          j = i - 1
          while j >= 0 and key < arr[j]:
              arr[j + 1] = arr[j]
              j -= 1
          arr[j + 1] = key
      return arr