new_contents: from assess_isoform_quantification.options import validate_file_option
  from tempfile import NamedTemporaryFile
  from schema import SchemaError
  
  import pytest
  
  
  def test_validate_file_option_returns_handle_for_file_that_exists():
      file = NamedTemporaryFile()
      file_name = file.name
      assert validate_file_option(file_name, "dummy") is not None
  
  
  def test_validate_file_option_raises_exception_for_non_existing_file():
      file = NamedTemporaryFile()
      file_name = file.name
      file.close()
      with pytest.raises(SchemaError):
          validate_file_option(file_name, "dummy")
  
  
  def test_validate_file_option_exception_message_contains_correct_info():
      file = NamedTemporaryFile()
      file_name = file.name
      file.close()
  
      msg = "dummy"
      with pytest.raises(SchemaError) as exc_info:
          validate_file_option(file_name, msg)
  
      exc_msg = exc_info.value.message
      assert msg in exc_msg
      assert file_name in exc_msg
  
subject: Add a few test cases for validate_file_option function.