JUnit expected exception not working as expected

Question

i am trying to test a private method inside an ActionListener. The method should throw an exception if an invalid url is passed: Heres the code of my test:

@Rule
public ExpectedException expectedException = ExpectedException.none();
Map<JLabel, JTextField> inputs;
ActionListener listener;
AddStationWindow window;
ArrayList<Station> stationsToDelete;

@Before
public void setUp() throws IllegalAccessException, NoSuchFieldException, 
InstantiationException, SQLException, ClassNotFoundException {
inputs = new HashMap<JLabel, JTextField>();
window = new AddStationWindow();
stationsToDelete = new ArrayList<>();
InitializeH2Database.initialiteDatabase();

}

@Test
public void saveStation() throws NoSuchFieldException, 
IllegalAccessException, MalformedURLException, NoSuchMethodException, 
InvocationTargetException {
  Field f = window.getClass().getDeclaredField("inputElements");
  f.setAccessible(true);
  LinkedHashMap<JLabel, JTextField> inputs = (LinkedHashMap<JLabel, 
  JTextField>) f.get(window);
  Field f2 = window.getClass().getDeclaredField("save");
  f2.setAccessible(true);
  JButton saveButton = (JButton) f2.get(window);
  inputs.get(window.getInputLabels().get(0)).setText("Testsender");
  inputs.get((window.getInputLabels().get(1))).setText("asdasdsa");
  ActionListener listener = saveButton.getActionListeners()[0];
  Method m = listener.getClass().getDeclaredMethod("saveStation");
  m.setAccessible(true);
  m.invoke(listener);
  expectedException.expect(MalformedURLException.class);
}


@After
public void tearDown() {
stationsToDelete.forEach(s -> 
H2DatabaseConnector.getInstance().deleteStation(s));
}

This is the tested method inside the ActionListener:

private boolean saveStation() {
List<JLabel> keys = new ArrayList<>();
for (Map.Entry<JLabel, JTextField> inputElement : inputElements.entrySet()) {
    keys.add(inputElement.getKey());
}
String stationName = inputElements.get(keys.get(0)).getText();
String urlString = inputElements.get(keys.get(1)).getText();
URL stationURL = null;
try {
    stationURL = new URL(urlString);
} catch (MalformedURLException e) {
    JOptionPane.showMessageDialog(window, "Invalid URL!", "URL 
    not valid", JOptionPane.ERROR_MESSAGE);
    e.printStackTrace();
    return false;
}
Station s = new Station(stationName, stationURL);
if (checkStation(s)) {
    return WebradioPlayer.addStation(s);
}
return false;
}

If i run the test, i can see that the stack tarce shows the malformed url exception with message no protocol: 'asdasdsa', but the test fails. Can someone explain me why? JUnit version is 4.

Answer 1

You have to set the expected exception before you call the code that actually does throw the exception.

Instead of

@Test
public void saveStation() throws ... {
    // code here
    expectedException.expect(MalformedURLException.class);
}

you should write the test method as

@Test
public void saveStation() throws ... {
    expectedException.expect(MalformedURLException.class);
    // code here
}

Additionally, you have to change your method saveStation to not suppress the exception if you actually want to have it thrown. See @Leviand's answer for more details.

Answer 2

Your test is failing because you are expecting an exception to be thrown (you said invalid url exception), but you are wrapping that exception into a try catch, then you are printing the stacktrace.

try {
    stationURL = new URL(urlString);
} catch (MalformedURLException e) {
    JOptionPane.showMessageDialog(window, "Invalid URL!", "URL 
    not valid", JOptionPane.ERROR_MESSAGE);
    e.printStackTrace();
    return false;
}

you have to add the trown declaration in your catch, or not catch it at all, ie:

} catch (MalformedURLException e) {
    JOptionPane.showMessageDialog(window, "Invalid URL!", "URL 
    not valid", JOptionPane.ERROR_MESSAGE);
    e.printStackTrace();
    throw new MalformedURLException(e);
}

and add the throw info to your method

private boolean saveStation() throws MalformedURLException{