public static Collection<File> getFileResourcesByExtension(String extension) {
        return Arrays.stream(getClassPathElements())
                .flatMap(elem -> internalGetFileResources(elem, Pattern.compile(".*\\." + extension + "$"))
                        .stream())
                .collect(Collectors.toSet());
    }
@Test
    public void getResourcesByExtensionExisting() {
        final Collection<File> retrieved = getFileResourcesByExtension("txt");
        commonVerifyCollectionWithExpectedFile(retrieved, TEST_FILE);
    }