code: def test_run_with_missing_input():
      builder = PromptBuilder(template="This is a {{ variable }}")
      res = builder.run()
      assert res == {"prompt": "This is a "}
  
imports: import pytest
  from haystack.components.builders.prompt_builder import PromptBuilder
label_desc: Use image node_id 5 for calling a global function with example usage: test_run_with_missing_input() without return types