@Test
public void testToBundleNameToFilesMap_IgnoreSubDir() {

  // preparation
  final Path ignorableBasePath= Paths.get("/some/path/src/main/resources");
  final List<File> resourceFiles= ImmutableList.of(
          ignorableBasePath.resolve("messages_de.properties").toFile(),
          ignorableBasePath.resolve("messages_en.properties").toFile(),
          ignorableBasePath.resolve("options.properties").toFile(),
          ignorableBasePath.resolve("options_en_US.properties").toFile(),
          ignorableBasePath.resolve("options_en_GB.properties").toFile()
  );
  // execution
  final ResourceBundleContentHelper helper= new ResourceBundleContentHelper(ignorableBasePath);
  final Map<String, Map<Language, File>> bundleNameToFilesMap = helper.toBundleNameToFilesMap(resourceFiles);
  System.out.println(bundleNameToFilesMap.keySet());
  // verification
  assertThat(bundleNameToFilesMap.keySet()).containsExactly("messages", "options");
  assertThat(bundleNameToFilesMap.get("messages")).containsKeys(Language.of("de"), Language.of("en"));
  assertThat(bundleNameToFilesMap.get("messages").get(Language.of("de"))).hasName("messages_de.properties");
  assertThat(bundleNameToFilesMap.get("messages").get(Language.of("en"))).hasName("messages_en.properties");
  assertThat(bundleNameToFilesMap.get("options")).containsKeys(Language.of(""), Language.of("en_US"), Language.of("en_GB"));
  assertThat(bundleNameToFilesMap.get("options").get(Language.of(""))).hasName("options.properties");
  assertThat(bundleNameToFilesMap.get("options").get(Language.of("en_US"))).hasName("options_en_US.properties");
  assertThat(bundleNameToFilesMap.get("options").get(Language.of("en_GB"))).hasName("options_en_GB.properties");
}