android - 使用 mockito 测试使用上下文的函数

Question

Android Studio 2.1.2

我正在尝试测试调用 loadNewsFeed 的 getJsonFromResource。我希望能够测试 2 种情况，一种是 loadNewsFeed 将返回一个空字符串，另一种是返回一些 json 字符串。

所以我试图模拟 loadNewsFeed 函数以返回一个空字符串。但是，当调用具体的 getJsonFromResource 时，它将调用真正的 loadNewsFeed 并导致空指针异常。这是我在解释我在做什么的测试评论中尝试过的:

@Test
public void shouldFailIfJSONStringIsEmpty() throws Exception {
    /* Mock Context class */
    Context context = mock(Context.class);
    /* initialize the concrete parseNewsFeed passing in the fake context */
    ParseNewsFeed parseNewsFeed = new ParseNewsFeed(context);
    /* Create a mock of the parseNewsFeed so a fake call to loadNewsFeed will return an empty string */
    ParseNewsFeed mockParseNewsFeed = mock(ParseNewsFeed.class);
    /* Mock the events that will be verified */
    ParseNewsFeedContract.Events<Status> mockEvents = mock(ParseNewsFeedContract.Events.class);

    /* Return an empty string when loadNewsFeed is called */
    when(mockParseNewsFeed.loadNewsFeed()).thenReturn("");

    /* Called the concrete getJsonFromResource */
    parseNewsFeed.getJsonFromResource(mockEvents);

    /* verify that onNewsFailure was called once and onNewsSuccess was never called */
    verify(mockEvents, times(1)).onNewsFailure(anyString());
    verify(mockEvents, never()).onNewsSuccess(any(Status.class));
}

这是我要测试的类(class)。

public class ParseNewsFeed implements ParseNewsFeedContract {
    private Context mContext;

    public ParseNewsFeed(Context context) {
        if(context != null) {
            Timber.d("mContext != null");
            mContext = context;
        }
    }

    /**
     * Get the json from the local resource file and add to the cache to save loading each time
     * @return the json in string representation
     */
    @Override
    public void getJsonFromResource(Events<Status> events) {
        /* Get the json in string format */
        final String jsonString = loadNewsFeed();

        /* Check that is contains something */
        if(!jsonString.isEmpty()) {
            try {
                final Status status = new Gson().fromJson(jsonString, Status.class);
                if(status != null) {
                    Timber.d("url: %s", status.getResults().get(0).getMultimedia().get(0).getUrl());
                    events.onNewsSuccess(status);
                }
                else {
                    Timber.e("status == null");
                    events.onNewsFailure("Failed to get results from json");
                }
            }
            catch (JsonSyntaxException e) {
                Timber.e("Invalid JSON: %s", e.getMessage());
                events.onNewsFailure(e.getMessage());
            }
        }
    }

    /**
     * Opens and reads from the news_list and writes to a buffer
     * @return return the json representation as a string or a empty string for failure
     */
    public String loadNewsFeed() {
        InputStream inputStream = mContext.getResources().openRawResource(R.raw.news_list);
        Writer writer = new StringWriter();
        char[] buffer = new char[1024];

        try {
            InputStreamReader inputReader = new InputStreamReader(inputStream, "UTF-8");
            BufferedReader bufferReader = new BufferedReader(inputReader);
            int n;
            while ((n = bufferReader.read(buffer)) != -1) {
                writer.write(buffer, 0, n);
            }

            inputStream.close();
        }
        catch (IOException ioException) {
            return "";
        }

        return writer.toString();
    }
}

Answer 1

首先，您的原始代码不起作用的原因是因为您的两个对象 parseNewsFeed 和 mockParseNewsFeed 之间没有关系，因此您所做的 stub 当您调用 parseNewsFeed.getJsonFromResource(mockEvents) 时，mockParseNewsFeed 没有任何效果。按照 David Wallace 的建议使用 spy 会奏效，但如果我是你，我会以不同的方式重写代码，以使其更易于测试。

一个观察是 loadNewsFeed() 方法中的代码似乎与 ParseNewsFeed 类没有很强的关系，所以我将这段代码提取到一个对象(例如 NewsFeedLoader)，然后将此对象作为 ParseNewsFeed 类的依赖项。然后您可以轻松地模拟此 Loader(返回 "" 或您在传递 Context 和可能的 R. raw.news_list id)。使用此 Loader 类，您甚至可以将它与 ParseNewsFeed 分开进行单元测试，并能够根据需要改进 Loader(例如一种读取原始资源的更好方法)而不影响 ParseNewsFeed 类。