### Question:
StringToUniqueIntegerMap extends SimpleStoredMap<Integer> { @Override public boolean save() { return store.save(); } StringToUniqueIntegerMap(String name);  StringToUniqueIntegerMap(String name, int maxId);  StringToUniqueIntegerMap(StringToUniqueIntegerMap parent, SimpleStore<Integer> store, int minId, int maxId, String name); int convertToParent(int localId); int convertTo(StringToUniqueIntegerMap other, int localId); int convertFrom(StringToUniqueIntegerMap other, int foreignId); int register(String key); boolean register(String key, int id); @Override String getString(Integer value); @Override Integer getValue(String key); @Override boolean save(); @Override Collection<String> getKeys(); @Override List<Pair<Integer, String>> getItems(); @Override void clear();  }### Answer:
@Test public void persistTest() { int numKeys = this.numKeys / 4; for (int i = 0; i < numKeys; i++) { registerWithWorld1Map("key1" + i); registerWithWorld2Map("key2" + i); } world1Map.save(); world2Map.save(); readWorldFiles(); for (int i = numKeys - 1; i >= 0; i--) { registerWithWorld1Map("key1" + i); registerWithWorld2Map("key2" + i); } world1File.delete(); world2File.delete(); }