### Question:
Utils { public static Set<String> stringToSet(String string) { if (string == null || string.isEmpty()) { return Collections.emptySet(); } return new HashSet<String>(Arrays.asList(string.split(" "))); }  static boolean isEmpty(final String s); static boolean isEmpty(final Collection<?> c); static boolean isEmpty(final Map<?, ?> m); static Set<String> splitResponseType(final String responseType); static Set<String> splitScope(final String scope); static String joinScope(final Set<String> scope); static Set<String> stringToSet(String string); static boolean isOpenIdConnectFragmentErrorType(Set<String> requestedResponseTypes); static boolean isOAuth2FragmentErrorType(Set<String> requestedResponseTypes); static boolean isOpenIdConnectClient(ClientRegistration clientRegistration); static UrlLocation getRequiredUrlLocation(OAuth2Request request, ClientRegistration clientRegistration); static UrlLocation getRequiredUrlLocation(Set<String> responseTypes, ClientRegistration clientRegistration); static List<T> asSortedList(Collection<T> collection,
                                                                         Comparator<? super T> comp);  }### Answer:
@Test public void shouldConvertStringToSetWhenStringIsNull() { assertEquals(Utils.stringToSet(null), Collections.emptySet()); }
@Test public void shouldConvertStringToSetWhenStringIsEmpty() { assertEquals(Utils.stringToSet(""), Collections.emptySet()); }
@Test public void shouldConvertStringToSet() { Set<String> expectedResponseTypes = new LinkedHashSet<String>(); expectedResponseTypes.add("a"); expectedResponseTypes.add("b"); expectedResponseTypes.add("c"); assertEquals(Utils.stringToSet("a b c"), expectedResponseTypes); }