### Question:
Utils { public static String joinTail(List<String> pathFragments) { return pathFragments.stream() .skip(1) .collect(Collectors.joining(PATH_DELIMITER)); }  static Object getSubdocumentValue(Document document, String key); static Object getSubdocumentValueCollectionAware(Document document, String key); static String getDatabaseNameFromFullName(String fullName); static String getCollectionNameFromFullName(String fullName); static boolean isTrue(Object value); static Number normalizeNumber(Number value); static void markOkay(Document result); static String join(List<?> values, String delimiter); static void changeSubdocumentValue(Object document, String key, Object newValue); static void validateFieldNames(Document document); static Object removeSubdocumentValue(Object document, String key); static String describeType(Object value); static String joinTail(List<String> pathFragments); static String firstFragment(String input); static List<String> splitPath(String input); static String getShorterPathIfPrefix(String path1, String path2); static List<String> collectCommonPathFragments(String path1, String path2); static String getHostName(); static void copySubdocumentValue(Document input, Document result, String key); static final String PATH_DELIMITER; }### Answer:
@Test void testJoinTail() throws Exception { assertThat(Utils.joinTail(Collections.singletonList("a"))).isEqualTo(""); assertThat(Utils.joinTail(Collections.emptyList())).isEqualTo(""); assertThat(Utils.joinTail(Arrays.asList("a", "b"))).isEqualTo("b"); assertThat(Utils.joinTail(Arrays.asList("a", "b", "c"))).isEqualTo("b.c"); assertThat(Utils.joinTail(Arrays.asList("a", "b", "c", "d"))).isEqualTo("b.c.d"); }