我正在发送一封带有thymeleaf模板引擎的邮件。当我没有使用thymeleaf时，邮件单元测试运行得很好，但是在我添加了thymeleaf之后，测试一直给我NullPointerException。下面是我从EmailService中得到的代码：

private JavaMailSender javaMailSender;
    private TemplateEngine templateEngine;

    public EmailServiceImpl(JavaMailSender javaMailSender, TemplateEngine templateEngine){
        this.javaMailSender = javaMailSender;
        this.templateEngine = templateEngine;
    }

    @Override
    public void sendEmail(Employee employee,String email) throws MessagingException {
        Context context = new Context();
        context.setVariable("employee",employee);

        String process = templateEngine.process("/email",context);

        MimeMessage message = javaMailSender.createMimeMessage();
        MimeMessageHelper helper;
        helper = new MimeMessageHelper(message, true);
        helper.setTo(email);
        helper.setSubject("Hello "+employee.getName());
        helper.setText(process,true);
        javaMailSender.send(message);

    }

这是我的测试：

@Autowired
     TemplateEngine templateEngine;

    static Context context;

    @Mock
    private JavaMailSender javaMailSender;

    @InjectMocks
    private EmailServiceImpl emailServiceImpl;

    private MimeMessage mimeMessage;
    private MimeMessageHelper helper;
    private String email;

    Employee employee;
    String process;

    @BeforeEach
    public void setUp() throws MessagingException {

        employee = new Employee("John Smith",
                20.0,"AB243", "A","B",
                LocalDateTime.now().plusDays(2),20);

        mimeMessage = new MimeMessage((Session)null);

        email = "someone@gmail.com";
        context = new Context();
        process = templateEngine.process("/email",context);
        helper.setText(process,true);

    }

    @Test
   public void emailTest() throws MessagingException {
       when(javaMailSender.createMimeMessage()).thenReturn(mimeMessage);
       String recipient = email;
        emailServiceImpl.sendEmail(employee,email);
        assertEquals(recipient, mimeMessage.getRecipients(MimeMessage.RecipientType.TO)[0].toString());
    }

所以我试着自动安装模板引擎，我试着初始化它，我试着设置助手属性，但是什么都不起作用。有人知道如何解决这个问题吗？谢谢！