input: Write a function to perform linear search on a given array and return the position of the search item if found, otherwise return -1. The function should take one argument which is the search item.
  
  # Example test cases
  assert linearSearch('school') == 0
  assert linearSearch('mall') == 3
  assert linearSearch('library') == -1
output: def linearSearch(search_item):
      array = ['school', 'park', 'store', 'mall', 'gym']
      for i in range(len(array)):
          if array[i] == search_item:
              return i
      return -1