Test exception of a method which contains try catch in junit - junit4

Question

I have code snippet below.
What I want is if getNames() method catch an exception
( ex. InterruptedException ),
want to check if Got InterruptedException !!! prints out or not.
There are some examples of testing exception for a method
which throws an exception in its method ( ex. String method1() throws InterruptedException {...} ) in the Internet.
But not this case. Does anyone have some thought or idea?
public class A {
public List<String> getNames()
{
String addess = "address1";
int age = 17;
List<String> names = null;
try {
names = getSomeNames(address, sex);
}
catch (InterruptedException | ExecutionException e) {
throw new MyCustomException(e);
}
catch(Exception e) {
throw new MyCustomException(e);
}
return names;
}
List<String> getSomeNames(String address, int sex) throws InterruptedException, ExecutionException
{
// ...
// throw exceptions... at some point
//
return names;
}
}
public class MyCustomException extends Exception {
public MyCustomException(Throwable e) {
if (e.getCause() instanceof InterruptedException) {
// write log
System.out.println("Got InterruptedException !!!");
}
else if (e.getCause() instanceof ExecutionException) {
// write log
System.out.println("Got ExecutionException!!!");
}
else {
// write log
}
}
}
I tried this but the test failed and got NullPointerException in catch block.
#Test
public void testException() {
A objA = spy(new A());
try {
doThrow(MyCustomException.class).when(objA).getNames();
objA.getNnames();
}
catch (Exception e) {
System.out.println(e.getCause().toString()); // ==> throws java.lang.NullPointerException here.
}
}

Answer 1

There are several ways to test it.
First solution is to replace System.out with different stream and read from it later. ( I don't like this approach )
#Test
void whenSayHi_thenPrintlnCalled() throws IOException {
PrintStream normalOutput = System.out;
String result;
try (ByteArrayOutputStream baos = new ByteArrayOutputStream(); PrintStream temporalOutput = new PrintStream(baos)) {
System.setOut(temporalOutput);
ThatGuy thatGuy = new ThatGuy();
thatGuy.sayHi();
result = new String(baos.toByteArray(), StandardCharsets.UTF_8);
} finally {
System.setOut(normalOutput);
}
assertEquals("Hi", result.trim());
}
Second one is to use logger instead of just System.out. I consider this approach better not only from testing, but from code design perspective as well. Using this one you can just replace logger with Mockito.mock and user Mockito.verify to check what was called on your logger.
#Test
void whenSayHi_thenCallLogger() {
Logger logger = Mockito.mock(Logger.class);
ThatGuy thatGuy = new ThatGuy();
ReflectionTestUtils.setField(thatGuy, "logger", logger);
thatGuy.sayHiToLog();
verify(logger).error("Hi");
}
Class under testing looks like this:
class ThatGuy {
private static Logger logger = LoggerFactory.getLogger(ThatGuy.class);
void sayHi() {
System.out.println("Hi");
}
void sayHiToLog() {
logger.error("Hi");
}
}