input: Write a function to tokenize a given text using the NLTK library. The function should take a string as input and return a list of tokens. 
  assert tokenize_text('Python is an interpreted, high-level, general-purpose programming language.')==['Python', 'is', 'an', 'interpreted', 'high', '-', 'level', 'general', '-', 'purpose', 'programming', 'language', '.']
  assert tokenize_text('Tokenization is the process of breaking text into smaller units called tokens.')==['Tokenization', 'is', 'the', 'process', 'of', 'breaking', 'text', 'into', 'smaller', 'units', 'called', 'tokens', '.']
  assert tokenize_text('')==[]
output: import nltk
  nltk.download('punkt')
  
  def tokenize_text(text):
      return nltk.word_tokenize(text)