### Question:
ConfigValueConfigSourceWrapper implements ConfigValueConfigSource, Serializable { @Override public Set<String> getPropertyNames() { return configSource.getPropertyNames(); } private  ConfigValueConfigSourceWrapper(final ConfigSource configSource); @Override ConfigValue getConfigValue(final String propertyName); @Override Map<String, ConfigValue> getConfigValueProperties(); @Override Map<String, String> getProperties(); @Override String getValue(final String propertyName); @Override Set<String> getPropertyNames(); @Override String getName(); @Override int getOrdinal();  }### Answer:
@Test public void getPropertyNames() { final Set<String> names = config().getPropertyNames(); assertEquals(1, names.size()); assertEquals("my.prop", names.iterator().next()); }