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('Hello world!')==['Hello', 'world', '!']
  assert tokenize_text('')==[]
  assert tokenize_text('Tokenization is fun.')==['Tokenization', 'is', 'fun', '.']
  assert tokenize_text('I love programming in Python.')==['I', 'love', 'programming', 'in', 'Python', '.']
output: def tokenize_text(text):
      from nltk.tokenize import word_tokenize
      return word_tokenize(text)