### Question:
MessagePanel extends JTextPane implements IMessageHandler { public synchronized void showMessage(final Throwable th, final ExceptionFormatter formatter) { if (th == null) { throw new IllegalArgumentException("th cannot be null"); } privateShowMessage(th, formatter, _saSetMessage); } MessagePanel(); void addToMessagePanelPopup(Action action); synchronized void showMessage(final Throwable th, 
                                        final ExceptionFormatter formatter); synchronized void showErrorMessage(final Throwable th, 
                                              ExceptionFormatter formatter); synchronized void showMessage(final String msg); void showWarningMessage(String msg); synchronized void showErrorMessage(final String msg);  }### Answer:
@Test (expected = IllegalArgumentException.class) public final void testShowMessageThrowableExceptionFormatter() { messagePanelUnderTest.showMessage(null, null); }
@Test (expected = IllegalArgumentException.class) public final void testShowMessageString() { messagePanelUnderTest.showMessage(null); }