@Test
  public void testProcess_from_var() {
    System.out.println("process fromvar");
    JMeterContext context = JMeterContextService.getContext();
    JMeterVariables vars = context.getVariables();

    SampleResult res = new SampleResult();
    res.setResponseData("".getBytes());
    context.setPreviousResult(res);

    vars.put("SVAR", json);

    JSONPathExtractor instance = new JSONPathExtractor();
    instance.setDefaultValue("DEFAULT");
    instance.setVar("test");
    instance.setJsonPath("$.store.book[*].author");
    instance.setSubject(JSONPathExtractor.SUBJECT_VARIABLE);
    instance.setSrcVariableName("SVAR");
    instance.process();
    assertEquals(
        "[\"Nigel Rees\",\"Evelyn Waugh\",\"Herman Melville\",\"J. R. R. Tolkien\"]",
        vars.get("test"));
  }