@Test(expected = FilesystemTrackerStartupException.class)
public void Should_throw_When_startCalledTwice()
        throws Exception {

    FilesystemTracker tracker = new FilesystemTracker(pathFilterMock, taskFactoryMock, fileSystemMock);
    try {
        tracker.start(directoryMock);
        verify(runnableMock, timeout(1000)).run();
    } catch (FilesystemTrackerStartupException e) {
        fail();
    }
    tracker.start(directoryMock);
}