code: def test_claude_2_1_pt_formatting():
      # Test case: User only, should add Assistant
      messages = [{"role": "user", "content": "Hello"}]
      expected_prompt = "\n\nHuman: Hello\n\nAssistant: "
      assert claude_2_1_pt(messages) == expected_prompt
  
      # Test case: System, User, and Assistant "pre-fill" sequence,
      #            Should return pre-fill
      messages = [
          {"role": "system", "content": "You are a helpful assistant."},
          {
              "role": "user",
              "content": 'Please return "Hello World" as a JSON object.',
          },
          {"role": "assistant", "content": "{"},
      ]
      expected_prompt = 'You are a helpful assistant.\n\nHuman: Please return "Hello World" as a JSON object.\n\nAssistant: {'
      assert claude_2_1_pt(messages) == expected_prompt
  
      # Test case: System, Assistant sequence, should insert blank Human message
      #            before Assistant pre-fill
      messages = [
          {"role": "system", "content": "You are a storyteller."},
          {"role": "assistant", "content": "Once upon a time, there "},
      ]
      expected_prompt = "You are a storyteller.\n\nHuman: \n\nAssistant: Once upon a time, there "
      assert claude_2_1_pt(messages) == expected_prompt
  
      # Test case: System, User sequence
      messages = [
          {"role": "system", "content": "System reboot"},
          {"role": "user", "content": "Is everything okay?"},
      ]
      expected_prompt = (
          "System reboot\n\nHuman: Is everything okay?\n\nAssistant: "
      )
      assert claude_2_1_pt(messages) == expected_prompt
  
imports: import sys
  import os
  from litellm import completion
  from litellm.llms.prompt_templates.factory import anthropic_pt, claude_2_1_pt, llama_2_chat_pt
label_desc: Use image node_id 2 for calling a global function with example usage: test_claude_2_1_pt_formatting() without return types