How to test FacesContext showing a message with JUnit

abort()-Method:

public void abort() {
    LOG.info("some-text");
    warning("some-text");
}

warning()-Method:

 public void warning(String message) {
    FacesContext.getCurrentInstance()
.addMessage(null, new FacesMessage(FacesMessage.SEVERITY_WARN, "INFO:", message));
}

I want to write a Test-Case for abort which is just verifying that nothing has changed and a second Test-Case which is verifying that warning() is working. I know these two little methods don't need a Unit-Test, but I want to know if it's possible. UI-Test for showing the p:message is working well but I want to check the Caption, Typ and Message by Unittest before because it's running much faster.

Solution

working solution with just using JUnit 4.11

Separate the content from warning() in a own class like this:

@Named
@RequestScoped
public class Resources {
       @Produces
       public FacesContext produceFacesContext() {
              return FacesContext.getCurrentInstance();
       }
}

Next you need to define an ArgumentCaptor which can catch the FacesMessage for your JUnit-Test. I´ve created it as a clss member which will be initialized in the @before section and get the null value in @teardown.

private ArgumentCaptor<FacesMessage> facesMessageCaptor;
@Before
public void setUp() {facesMessageCaptor = ArgumentCaptor
            .forClass(FacesMessage.class);
}
@After
public void tearDown() { facesMessageCaptor = null; }

Now you just need to add two @Mocks to your test-class

@Mock
Resources resourcesMock; 
@Mock
FacesContext facesContextMock;

So you did it! Write the test like this:

Mockito.doReturn(facesContextMock).when(resourcesMock).produceFacesContext();
// Execute Method
cut.warning("SOME_DETAIL_TEXT");
// Verify interactions with the Resources and Faces and maybe others...
verify(resourcesMock).produceFacesContext();
verify(facesContextMock).addMessage(Mockito.anyString() ,
                facesMessageCaptor.capture());
verifyNoMoreInteractions(...., resourcesMock, facesContextMock);
// write assert (i´ve used hamcrast-corematchers - more readable)
actualMessage = (FacesMessage) facesMessageCaptor.getValue();
assertThat(FacesMessage.SEVERITY_WARN, is(equalTo(actualMessage.getSeverity())));
assertThat(MY_TITLE, is(equalTo(actualMessage.getSummary())));
assertThat("DETAIL_TEXT", is(equalTo(actualMessage.getDetail())));