input: Write a function to tokenize a given text using the nltk library in Python. The function should take a string as input and return a list of tokens. If the input text is empty, the function should return an empty list.
  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('')==[]
  assert tokenize_text('Hello World!')==['Hello', 'World', '!']
  assert tokenize_text('Testing 1, 2, 3.')==['Testing', '1', ',', '2', ',', '3', '.']
output: def tokenize_text(text):
      if not text:
          return []
      return nltk.word_tokenize(text)