如何在Junit测试中避免FaceContext中出现NullPointerException？

Question

My team and me made a Webapp in Spring as a project and we have to test most of our code. The problem is that we use FaceContext messages in quite a lot of methods and always when we try to test those methods we get NullPointerException s at the FaceContext-Messages. How can i avoid or catch them?

Our current solution is to use @Test(expect = NullPointerException.class) but that is not really the way we want to go. Is this possible in Junit or do i need Selenium for this?

An example would be:

public boolean validateInfo(){
    boolean correct = true;
    if(startDate == null || endDate == null) {
        if(startDate == null)
   FacesContext.getCurrentInstance().addMessage("msg", new FacesMessage(FacesMessage.SEVERITY_ERROR, "Gib ein Startdatum an!", ""));
        if(endDate == null)             FacesContext.getCurrentInstance().addMessage("msg", new FacesMessage(FacesMessage.SEVERITY_ERROR, "Gib ein Enddatum an!", ""));

        return false;
    }
    if(startDate.after(endDate)) {
        FacesContext.getCurrentInstance().addMessage("msg", new FacesMessage(FacesMessage.SEVERITY_ERROR, "Startdatum muss vor dem Enddatum sein!", ""));
        correct = false;
    }

    if(maxChildren < 1) {
        FacesContext.getCurrentInstance().addMessage("msg", new FacesMessage(FacesMessage.SEVERITY_ERROR, "Max. Kinderanzahl muss größer 0 sein!", ""));
        correct = false;
    }

    if(bringTime.after(pickupTime)) {
        FacesContext.getCurrentInstance().addMessage("msg", new FacesMessage(FacesMessage.SEVERITY_ERROR, "Bringzeit muss vor dem Abholzeit sein!", ""));
        correct = false;
    }
    return correct;
}

It goes to the first FaceContext Message and throws a NullPointerException . Can someone help? Other solutions here on StackOverflow haven't helped.

Answer 1

Simple: your production code is calling a static method that probably returns null.

You could use frameworks such as PowerMock or JMockit to mock that static call.

Of course, the better way would be to avoid that static call and rely on dependency injection instead. As mocking static stuff is considered a bad practice. So the better approach would be to change your production code to be easier to test, instead of turning to such frameworks to "fix" your design problem.

Answer 2

the problem is that a facesContext is not a singleton, and starts a request upon running. Junit wont be able to handle that request by itself, itll need to be mocked up, or stubbed in. see more about facescontext here

http://illegalargumentexception.blogspot.com/2011/12/jsf-mocking-facescontext-for-unit-tests.html

and here is the javadoc http://docs.oracle.com/javaee/6/api/javax/faces/context/FacesContext.html

Answer 3

To add to @JasonD, Its advised to passing FacesContext#getCurrentInstance() as to calling it, since it has performance and functionality implication.

Also don't bundle validation logic directly into your code, use JSR 349 - Bean Validation- as it defines a metadata model and API for entity and method validation.

Hibernate has an implementation and a good documentation on testing validation constraints