public int act() {
Object key1 = "1";
Object key2 = "2";
Object key3 = "3";
NativeObject instance = new NativeObject();
NativeArray<String> set1 = new NativeArray(instance.keys());
assert set1.length() == 0;
Object value1 = instance.setProperty(key1, "value1");
Object value2 = instance.setProperty(key2, "value2");
Object value3 = instance.setProperty(key3, "value3");
NativeArray<String> set2 = new NativeArray(instance.keys());
assert set2.length() == 3;
assert set2.indexOf(key1) != -1;
assert set2.indexOf(key2) != -1;
assert set2.indexOf(key3) != -1;
assert set2.indexOf("4") == -1;
instance.deleteProperty(key1);
instance.deleteProperty(key3);
NativeArray<String> set3 = new NativeArray(instance.keys());
assert set3.length() == 1;
assert set3.indexOf(key1) == -1;
assert set3.indexOf(key2) != -1;
assert set3.indexOf(key3) == -1;