### Question:
AbstractConfig { public Set<String> unused() { Set<String> keys = new HashSet<>(originals.keySet()); keys.removeAll(used); return keys; } @SuppressWarnings("unchecked")  AbstractConfig(ConfigDef definition, Map<?, ?> originals, boolean doLog);  AbstractConfig(ConfigDef definition, Map<?, ?> originals); void ignore(String key); Short getShort(String key); Integer getInt(String key); Long getLong(String key); Double getDouble(String key); @SuppressWarnings("unchecked") List<String> getList(String key); Boolean getBoolean(String key); String getString(String key); ConfigDef.Type typeOf(String key); Password getPassword(String key); Class<?> getClass(String key); Set<String> unused(); Map<String, Object> originals(); Map<String, String> originalsStrings(); Map<String, Object> originalsWithPrefix(String prefix); Map<String, Object> valuesWithPrefixOverride(String prefix); Map<String, ?> values(); void logUnused(); T getConfiguredInstance(String key, Class<T> t); List<T> getConfiguredInstances(String key, Class<T> t); List<T> getConfiguredInstances(String key, Class<T> t, Map<String, Object> configOverrides); @Override boolean equals(Object o); @Override int hashCode();  }### Answer:
@Test public void testUnused() { Properties props = new Properties(); String configValue = "org.apache.kafka.common.config.AbstractConfigTest$ConfiguredFakeMetricsReporter"; props.put(TestConfig.METRIC_REPORTER_CLASSES_CONFIG, configValue); props.put(FakeMetricsReporterConfig.EXTRA_CONFIG, "my_value"); TestConfig config = new TestConfig(props); assertTrue("metric.extra_config should be marked unused before getConfiguredInstances is called", config.unused().contains(FakeMetricsReporterConfig.EXTRA_CONFIG)); config.getConfiguredInstances(TestConfig.METRIC_REPORTER_CLASSES_CONFIG, MetricsReporter.class); assertTrue("All defined configurations should be marked as used", config.unused().isEmpty()); }