如何编写静态 void 方法的单元测试

Question

我遇到一个问题，我不知道如何编写静态 void 方法的单元测试。

我现在有一个使用 Apache HttpClient 的 HttpHelper 类。如下代码。

public class HttpHelper {
    private static CloseableHttpClient httpClient;

    public static void init() {
        httpClient = HttpClients.custom().setSSLContext(getDummySSL()).build();
    }

    public static void closeHttpClient() throws IOException {
        httpClient.close();
    }

    private static SSLContext getDummySSL() {
        ...omit
    }

    private static void send() {
        HttpGet httpGet = new HttpGet("https://someUrl.com");

        try(CloseableHttpResponse httpResponse = httpClient.execute(httpGet)) {
            if(httpResponse.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
                responseString = EntityUtils.toString(httpResponse.getEntity());
                // do something
            } else {
                throw new Exception();
            }
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

所以我主要调用HttpHelper.init() 来初始化httpClient。每次我想发送请求时，我都会致电HttpHelper.send()。因为我不想每次都创建一个新的 httpClient 。最后我会调用HttpHelper.close()关闭httpClient。

我想知道如何测试那些 void 方法。我的概念是在我的测试中创建一个CloseableHttpClient，然后调用HttpHelper.init() 来创建实际的。然后比较我的预期和实际的是否相同。我说的对吗？

由于变量和方法被声明为静态。编写单元测试有点困难。有很多帖子说将方法设为静态是一种不好的做法。但是在我的示例中，我不知道如何避免将它们声明为静态并保留单个 CloseableHttpClient 实例。

谢谢！

Answer 1

单实例保证主要通过单例模式解决。单元测试的一个常见技巧是创建一个具有受保护可见性的构造函数，您可以在其中放置用于测试的参数。这个类终于可以变成这样了。

public class HttpHelper {
    private static HttpHelper INSTANCE = new HttpHelper();

    public static HttpHelper getInstance() {
        return INSTANCE;
    }


    private CloseableHttpClient httpClient;

    private HttpHelper() {
        SSLContext sslContext = getDummySSL();
        this(HttpClients.custom().setSSLContext(sslContext).build(), sslContext);
    }

    protected HttpHelper(CloseableHttpClient httpClient, SSLContext sslContext) {
        this.httpClient = httpClient;
    }

    public void closeHttpClient() throws IOException {
        httpClient.close();
    }

    private static SSLContext getDummySSL() {
        ...
    }

    private void send() {
        ...
    }
}

我还将getDummySSL 重命名为createDummySSL，但这是细节。

Answer 2

拥有一个如此静态的类是不好的，因为很难测试它。我理解你为什么想要这个，但你可以享受所有同样的好处：

public class HttpHelper {

    private static HttpHelper DEFAULT_INSTANCE = null;

    private CloseableHttpClient httpClient;

    public HttpHelper(CloseableHttpClient httpClient) {
        this.httpClient = httpClient;
    }

    public static void getDeafultInstance() { // this should probably be synchronised for thread safety
        if (DEFAULT_INSTANCE == null) {
            DEFAULT_INSTANCE = httpClient = HttpClients.custom().setSSLContext(getDummySSL()).build();
        }
        return DEAFULT_INSTANCE;
    }

    private static SSLContext getDummySSL() {
        ...omit
    }

    public void closeHttpClient() throws IOException {
        httpClient.close();
    }

    private void send() {
        HttpGet httpGet = new HttpGet("https://someUrl.com");

        try(CloseableHttpResponse httpResponse = httpClient.execute(httpGet)) {
            if(httpResponse.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
                responseString = EntityUtils.toString(httpResponse.getEntity());
                // do something
            } else {
                throw new Exception();
            }
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

然后你可以像这样对它进行单元测试：

public class HttpHelperTest {

    @Test
    public testSendsRequestToSomeUrl() {
        CloseableHttpClient httpClientMock = mock();
        when(httpClient.execute(any())).thenReturn(..http_response_where_stauts_code_is_ok..)
        HttpHelper httpHelper = new HttpHelper(httpClientMock)
        httpHelper.send()
        verify(httpClient).execute(new HttpGet("https://someUrl.com"))
    }

}

并像这样在实际代码中使用它：

HttpHelper.getDeafultInstance().send()

附言

如果您有某种可用的依赖注入框架，那么您可以完全摆脱静态方法。