input: Write a python function to search for books using a given search term from the Google Books API, and return the results in JSON format.
  assert isinstance(search_books('python'), list)
  assert 'title' in search_books('flask')[0]['volumeInfo']
  assert 'authors' in search_books('machine learning')[0]['volumeInfo']
output: import requests
  
  def search_books(search_term):
      url = "https://www.googleapis.com/books/v1/volumes"
      params = {"q": search_term}
      response = requests.get(url, params=params)
      results = response.json().get('items', [])
      return results