### Question:
JavaxJson { @SuppressWarnings("WeakerAccess") public static Optional<JsonObject> optObject(final JsonObject json, final String key) { return Optional.ofNullable(json.get(key)).filter(JsonObject.class::isInstance).map(JsonObject.class::cast); } private  JavaxJson(); static boolean nonEmptyValue(final @Nullable JsonValue value); static boolean nonDefaultValue(final @Nullable JsonValue value, final @NotNull JsonValue defaultValue); static JsonValue wrap(final Object object); @SuppressWarnings("WeakerAccess") static Object unwrap(final JsonValue jsonValue); @SuppressWarnings("WeakerAccess") static Map<String, Object> unwrapObject(final JsonObject jsonObject); @SuppressWarnings("WeakerAccess") static List<Object> unwrapArray(final JsonArray jsonArray); static @NotNull JsonObject shallowMergeObjects(final @Nullable JsonObject base,
                                                          final @Nullable JsonObject overlay); static Value val(Object value); static Obj obj(final Key... keys); static Obj obj(final JsonObject jsonObject); static Obj obj(final Map<?, ?> map); static Key key(final String key, final Object value); static KeyCursor key(final String key); static Arr arr(Object... values); @SuppressWarnings("WeakerAccess") static Optional<JsonObject> optObject(final JsonObject json, final String key); @SuppressWarnings("WeakerAccess") static JsonObject objectOrEmpty(final JsonObject json, final String key); @SuppressWarnings("WeakerAccess") static Optional<JsonArray> optArray(final JsonObject json, final String key); static JsonArray arrayOrEmpty(final JsonObject json, final String key); static List<String> mapArrayOfStrings(final JsonArray jsonArray); static List<R> mapArrayOfStrings(final JsonArray jsonArray,
                                                final Function<String, R> mapFunction); static List<R> mapArrayOfStrings(final JsonArray jsonArray,
                                                final Function<String, R> mapFunction,
                                                final boolean discardNulls); static List<R> mapArrayOfObjects(final JsonArray jsonArray,
                                                final Function<JsonObject, R> mapFunction); static List<R> mapArrayOfObjects(final JsonArray jsonArray,
                                                final Function<JsonObject, R> mapFunction,
                                                final boolean discardNulls); static List<R> mapObjectValues(final JsonObject jsonObject,
                                              final BiFunction<String, JsonObject, R> mapBiFunction,
                                              final boolean discardNulls); @SuppressWarnings("WeakerAccess") static List<R> parseFromArray(final @NotNull JsonArray jsonArray,
                                             final @NotNull Fun.ThrowingFunction<String, R> parser,
                                             final @Nullable BiConsumer<String, Exception> errorConsumer); static boolean hasNonNull(final @NotNull JsonObject json, final String key); @SuppressWarnings("WeakerAccess")
    static final Function<JsonValue, String> JSON_VALUE_STRING; }### Answer:
@Test public void testOptObject() { assertFalse("empty object returns empty object for any key", optObject(JsonValue.EMPTY_JSON_OBJECT, "someKey").isPresent()); assertFalse("object returns empty object for present key with non-object value", optObject(key("someKey", arr()).get(), "someKey").isPresent()); assertFalse("object returns empty object for present key with null value", optObject(key("someKey", null).get(), "someKey").isPresent()); assertTrue("object returns present object for present key with object value", optObject(key("someKey", key("foo", "bar")).get(), "someKey").isPresent()); assertEquals("object returns correct object value for key with object value", "bar", optObject(obj() .key("someKey", key("foo", "bar")) .key("otherKey", key("bar", "foo")).get(), "someKey") .map(object -> object.getString("foo")).orElse("")); }