### Question:
CredentialTypes { public static <T> String credentialTypeOf(T input) { Class<?> authenticationType = input.getClass(); CredentialType credentialType = findCredentialType(authenticationType); checkArgument(credentialType != null, "programming error: %s should have annotation %s", authenticationType, CredentialType.class.getName()); return credentialType.value(); }  static String credentialTypeOf(T input); static Map<String, T> indexByCredentialType(Iterable<T> iterable); static CredentialType findCredentialType(Class<?> input); static final String API_ACCESS_KEY_CREDENTIALS; static final String PASSWORD_CREDENTIALS; static final String TOKEN_CREDENTIALS; }### Answer:
@Test(expectedExceptions = IllegalArgumentException.class) public void testCredentialTypeOfWithoutAnnotation() { CredentialTypes.credentialTypeOf(""); }