### Question:
FunctionRegistryHolder { public String getJarNameByFunctionSignature(String functionName, String functionSignature) { try (AutoCloseableLock lock = readLock.open()) { for (Map.Entry<String, Map<String, Queue<String>>> jar : jars.entrySet()) { Queue<String> functionSignatures = jar.getValue().get(functionName); if (functionSignatures != null && functionSignatures.contains(functionSignature)) { return jar.getKey(); } } } return null; } FunctionRegistryHolder(); long getVersion(); void addJars(Map<String, List<FunctionHolder>> newJars, long version); void removeJar(String jarName); List<String> getAllJarNames(); List<String> getFunctionNamesByJar(String jarName); ListMultimap<String, DrillFuncHolder> getAllFunctionsWithHolders(AtomicLong version); ListMultimap<String, DrillFuncHolder> getAllFunctionsWithHolders(); ListMultimap<String, String> getAllFunctionsWithSignatures(); List<DrillFuncHolder> getHoldersByFunctionName(String functionName, AtomicLong version); List<DrillFuncHolder> getHoldersByFunctionName(String functionName); boolean containsJar(String jarName); int functionsSize(); String getJarNameByFunctionSignature(String functionName, String functionSignature);  }### Answer:
@Test public void testJarNameByFunctionSignature() { FunctionHolder functionHolder = newJars.get(built_in).get(0); assertEquals("Jar name should match", built_in, registryHolder.getJarNameByFunctionSignature(functionHolder.getName(), functionHolder.getSignature())); assertNull("Jar name should be null", registryHolder.getJarNameByFunctionSignature("unknown_function", "unknown_function(unknown-input)")); }