input: Write a function to replace all occurrences of a character in a string with the provided replacement character. The function should return the modified string.
  
  def replace_all_occurrences(str, char, replacement):
    return str.replace(char, replacement)
  
  assert replace_all_occurrences("Hello World!", 'l', 'X')=="HeXXo WorXd!"
  assert replace_all_occurrences("Python Programming", 'o', 'a')=="Pythan Pragramming"
  assert replace_all_occurrences("This is a test", 's', 'z')=="Thiz iz a tezt"
  assert replace_all_occurrences("Hello World!", ' ', '-')=="Hello-World!"
  assert replace_all_occurrences("", 'a', 'b')==""
output: def replace_all_occurrences(str, char, replacement):
    return str.replace(char, replacement)