### Question:
ConfigSourceMap extends AbstractMap<String, String> implements Map<String, String>, Serializable { public boolean isEmpty() { return delegate.getPropertyNames().isEmpty(); } ConfigSourceMap(final ConfigSource delegate); int size(); boolean isEmpty(); boolean containsKey(final Object key); String get(final Object key); Set<String> keySet(); Collection<String> values(); Set<Entry<String, String>> entrySet(); void forEach(final BiConsumer<? super String, ? super String> action);  }### Answer:
@Test public void testIsEmpty() { assertTrue(new ConfigSourceMap(new PropertiesConfigSource(Collections.emptyMap(), "test", 100)).isEmpty()); assertFalse(new ConfigSourceMap(ONE_CONF_SRC).isEmpty()); assertFalse(new ConfigSourceMap(MANY_CONF_SRC).isEmpty()); }