Added basic program and unit test script

# program.py

import os

def main():

  filename = 'test_file.txt'

  try:

      with open(filename, 'r') as file_in:

          content = file_in.read()

      messages = [f'Found file {filename}', f'That contains {content}']

      print('\n'.join(messages))

  except FileNotFoundError:

      print(f'Creating file {filename}')

      with open(filename, 'w') as file_out:

          file_out.write('empty')

  if (value:= os.getenv('GLOBAL_VAR_FOR_CI')) is not None:

    return f'Hello, {value}!'

  else:

    return('Hello, GitLab CI/CD!')

if __name__ == "__main__":

  out = main()

  print(out)

# test_program.py

import unittest

from program import main

class TestStringMethods(unittest.TestCase):

  def test_output(self):

    res = main()

    self.assertEqual('Hello, GitLab CI/CD!', res)

if __name__ == '__main__':

    unittest.main()