当我尝试判断response.getContenttype()的返回值时,运行控制台将显示：

java.lang.AssertionError: 
Expected :text/plain
Actual   :null

但是当我尝试判断stringWriter()的返回值时,可以：

Process finished with exit code 0

源代码：

业务代码段：

设置内容类型：

@Override
public void doPost(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    request.setCharacterEncoding("utf-8");

    response.setContentType("text/plain");
    response.setHeader("Cache-Control", "no-cache");
    response.setCharacterEncoding("utf-8");

    process(request, response);
}

编写printWriter：

@Override
protected void process(HttpServletRequest request, HttpServletResponse response) throws
    ServletException, IOException {
    JSONObject resultObject = queryMXRatioData(request);
    response.getWriter().write(resultObject.toJSONString());
}

测试类别：

public class TestServlet extends Mockito {
private HttpServletRequest request = mock(HttpServletRequest.class);
private HttpServletResponse response = mock(HttpServletResponse.class);
private HttpSession session = mock(HttpSession.class);
private StringWriter stringWriter = new StringWriter();
private PrintWriter printWriter = new PrintWriter(stringWriter);

@Before
public void setup() throws Exception {
    when(request.getParameter("start")).thenReturn("0");
    when(request.getSession()).thenReturn(session);
    when(response.getWriter()).thenReturn(printWriter);
}

@Test
public void testGetContentType() throws Exception {
    new MXRatioDataLoader().doPost(request, response);

    assertEquals("text/plain", response.getContentType());
}

@Test
public void testStringWriter() throws Exception {
    new MXRatioDataLoader().doPost(request, response);
    String expect = "{\"total\":1,\"data\":[{\"U\":\"230.36575\",\"LOWLIMIT\":\"200\",\"OID\":\"5629499552628739\",\"NAME\":\"220kV\",\"RATIO\":\"104.7%\",\"LIMIT\":\"250\"}]}";
    assertEquals(expect, stringWriter.toString());
}

解决方法:

因为HttpServletResponse是模拟的,所以调用的代码

response.setContentType("text/plain");

是无人操作；模拟没有状态,除了记录它发生的情况外,没有对set调用执行任何操作.

更好的测试是验证是否进行了适当的调用,即

new MXRatioDataLoader().doPost(request, response);
verify(response).setContentType("text/plain");