assertThrows usage in JUnit - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of assertThrows in JUnit?

assertThrows checks if a specific exception is thrown by a block of code during a test. It helps verify error handling.

beginner

How do you write a basic assertThrows statement in JUnit 5?

Use assertThrows(ExceptionClass.class, () -> { /* code that throws */ }); to test if the exception occurs.

intermediate

What does assertThrows return and how can it be used?

It returns the thrown exception object, allowing you to check its message or properties for more detailed assertions.

intermediate

Why is assertThrows preferred over try-catch blocks in tests?

assertThrows makes tests cleaner and clearer by directly expressing the expected exception without manual try-catch handling.

beginner

Can assertThrows be used to test checked and unchecked exceptions?

Yes, it works for both checked exceptions (like IOException) and unchecked exceptions (like NullPointerException).

What is the correct way to use assertThrows to check for a NullPointerException?

A assertThrows(NullPointerException.class, () -> methodThatThrows());

B assertThrows(() -> methodThatThrows(), NullPointerException.class);

C assertThrows(methodThatThrows(), NullPointerException.class);

D assertThrows(NullPointerException, methodThatThrows());

The correct syntax is assertThrows(ExceptionClass.class, Executable), so option A is correct.

What does assertThrows return after catching the exception?

A The method return value

B A boolean true

C The exception object thrown

D Nothing (void)

assertThrows returns the caught exception object for further checks.

Which of these is NOT a benefit of using assertThrows in tests?

A Automatically fixes bugs

B Directly checks for exceptions

C Cleaner test code

D Avoids manual try-catch

assertThrows helps test exceptions but does not fix bugs automatically.

Can assertThrows be used to test if no exception is thrown?

A Yes, it passes if no exception is thrown

B Yes, but only for checked exceptions

C No, it ignores exceptions

D No, it fails if no exception is thrown

assertThrows expects an exception; if none is thrown, the test fails.

Which JUnit version introduced assertThrows?

A JUnit 4

B JUnit 5

C JUnit 3

D JUnit 6

assertThrows was introduced in JUnit 5 for better exception testing.

Explain how to use assertThrows to test that a method throws an IllegalArgumentException.

Think about the syntax: assertThrows(ExceptionClass.class, executable)

Why is using assertThrows better than a try-catch block in JUnit tests?

Consider how test code looks with and without assertThrows