input: Write a python function to concatenate two strings.
  assert joinStrings('Hello', 'World') == 'HelloWorld'
  assert joinStrings('Good', 'Bye') == 'GoodBye'
  assert joinStrings('Python', 'Programming') == 'PythonProgramming'
output: def joinStrings(str1, str2):
      return str1 + str2