<human>:  What is a good Python function to add suffix to filename.
<bot>: Here is a Python function to add suffix to filename

import os

def add_suffix(filename, suffix):
  """
  Adds a suffix to a filename
  :param filename: string
  :param suffix: string
  :return: string
  """
  return filename + suffix

# Enter the filename
filename = "test.txt"

# Enter the suffix
suffix = ".txt"

# Calling the function
filename_with_suffix = add_suffix(filename, suffix)

# Printing the filename
print(filename_with_suffix)

#Example Output
# test.txt.txt

#Remember to inspect code for bugs.