Mockito單元測試中的NullPointerException

Question

這是我要進行單元測試的SendEmail類。 我在下面顯示的行上收到NullPointerException，但是我不知道為什么。

另外，我是否正確組織了代碼？ 我不確定我是否正確使用了模仿。

public class StatsTest extends AbstractTestCase {
    @Mock
    MultiPartEmail MultiPartEmailMock;
    StatsTest statsTestObj;
    SendEmail mockedEmail;

    @Before
    public void setUp() throws Throwable {
        super.setUp();
        MockitoAnnotations.initMocks(this);
    }

    @Test(expected = ValidationException.class)
    public void testSendEmail() throws EmailException, IOException {
        MultiPartEmail multiPartEmailMock;
        SendEmail mockedEmail = Mockito.mock(SendEmail.class);
        Mockito.when((mockedEmail.getHtmlEmail()).send()) 
            .thenThrow(new ValidationException("Could not send the Email."));

        ^^ the line above is where the null pointer error is

        mockedEmail.sendEmail();
    }
}

這是要測試的課程：

public class SendEmail {
    private StringBuilder emailBody;
    private String senderEmail;
    private ArrayList<String> receiversEmails;
    private String emailSubject;
    private String hostName;
    private MultiPartEmail htmlEmail;

    public SendEmail(StringBuilder emailBody, String senderEmail, ArrayList<String> 
        receiversEmails, String emailSubject, String hostName, MultiPartEmail htmlEmail) {
        this.setEmailBody(emailBody);
        this.setSenderEmail(senderEmail);
        this.setReceiversEmails(receiversEmails);
        this.setEmailSubject(emailSubject);
        this.setHostName(hostName);
        this.setHtmlEmail(htmlEmail);
    }

    public void sendEmail()throws IOException, EmailException{

        htmlEmail.setHostName(getHostName());
        htmlEmail.addTo(getReceiversEmails().get(0));
        for(int i=0; i<getReceiversEmails().size(); i++){
            htmlEmail.addCc(getReceiversEmails().get(i));   
        }
        htmlEmail.setFrom(getSenderEmail());
        htmlEmail.setSubject(getEmailSubject());
        htmlEmail.setMsg((getEmailBody()).toString());
        htmlEmail.send();
    }
}

Answer 1

我認為您對需要測試和模擬的內容有些困惑。 Mockito提供了創建模擬對象的不同方法，例如： @Mock或Mockito.mock() 。 還有多種方法可以將這些模擬對象注入到要測試的類中，以便對該類進行單元測試。

如果沒有異常或其他類的所有詳細信息，這將不是一個完整的答案，但是我希望它可以幫助您清除一些概念。

注意：以下內容可能無法編譯，但希望您能理解。

public class StatsTest extends AbstractTestCase {
    @Mock MultiPartEmail mockMultiPartEmail; // this mock will be used in the instantiaion of the class under test
    SendEmail sendEmail; // renamed as this is not a mock, it is the class under test

    // define some things we can make assertions against (probably in some other tests...)
    private static final StringBuilder BODY = new StringBuilder("body");
    private static final String SENDER = "sender@foo.com";
    private static final Collection<String> RECIPIENTS = Arrays.asList("recepient@foo.com")
    private static final String SUBJECT = "subject";
    private static final String HOSTNAME = "hostname";

    @Before
    public void setUp() throws Throwable {
        super.setUp();
        MockitoAnnotations.initMocks(this); // will instantiate "mockMultiPartEmail"

        // instantiate our class under test
        sendEmail = new SendEmail(BODY, SENDER, RECIPIENTS, SUBJECT, HOSTNAME, mockMultiPartEmail);
    }

    @Test(expected = ValidationException.class)
    public void testSendEmail() throws EmailException, IOException {
        // given some condition
        Mockito.when(mockMultiPartEmail.send()).thenThrow(new ValidationException("Could not send the Email."));

        // when the method under test is called
        sendEmail.sendEmail();

        // then the exception will be thrown (and you have correctly expected this on the @Test annotation)
    }
}