input: Write a function to send an email using the smtplib library.
  assert send_email('test_sender@example.com', 'test_recipient@example.com', 'Test Subject', 'Test Message') == None
  assert send_email('user1@example.com', 'user2@example.com', 'Hello', 'This is a test email.') == None
output: def send_email(sender, recipient, subject, message):
      import smtplib
      from email.mime.text import MIMEText
      from email.mime.multipart import MIMEMultipart
  
      # Create the email message
      msg = MIMEMultipart()
      msg['From'] = sender
      msg['To'] = recipient
      msg['Subject'] = subject
      msg.attach(MIMEText(message, 'plain'))
  
      try:
          # Establish a secure session with the SMTP server
          server = smtplib.SMTP('smtp.example.com', 587)
          server.starttls()
  
          # Login to the email account
          server.login('your_email@example.com', 'your_password')
  
          # Send the email
          server.sendmail(sender, recipient, msg.as_string())
  
          # Terminate the SMTP session and close the connection
          server.quit()
      except Exception as e:
          print(f"Failed to send email: {e}")
          return
  
      return