def reverse(strng):
    xs =0
    i = (len(strng)-1)
    reversed_strng = ""

    while xs < len(strng): #0 to 4 since length is 5..
        reversed_strng = reversed_strng+strng[i]  #"" + strng[4] = y.. reversed_strng = y+p
        xs +=1
        i -= 1
    return reversed_strng


def test_cases():
    test(reverse("happy") == "yppah")
    test(reverse("Python") == "nohtyP")
    test(reverse("") == "")
    test(reverse("a") == "a")


def test(is_true):
    if is_true == True:
        print("Test Pass")
    else:
        print("test fail")

test_cases()