public static Set<File> findJsonFiles(File rootDir, Set<File> files) {
        return findJsonFiles(rootDir, files, (f) -> true);
    }
@Test
    public void testFindJsonFiles() throws Exception {
        Path dir = ResourceUtils.getResourceAsFile("json").toPath();
        List<String> jsonFiles;
        try (Stream<Path> stream = PackageHelper.findJsonFiles(dir)) {
            jsonFiles = stream
                    .map(PackageHelper::asName)
                    .toList();
        }

        assertTrue(jsonFiles.contains("a"), "Files a.json must be found");
        assertTrue(jsonFiles.contains("b"), "Files b.json must be found");
        assertFalse(jsonFiles.contains("c"), "File c.txt must not be found");
    }