Checking exception message in JUnit - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of checking an exception message in a test?

To verify that the code throws the correct error with the expected message, ensuring the error is meaningful and specific.

beginner

How do you check an exception message using JUnit 5's assertThrows?

Use assertThrows to catch the exception, then assert the message with getMessage(), for example:<br>

Exception exception = assertThrows(Exception.class, () -> method());<br>assertEquals("Expected message", exception.getMessage());

intermediate

Why is it better to check the exception message instead of only the exception type?

Because the message gives more detail about the error cause, helping to confirm the exact failure reason, not just the error category.

beginner

What happens if the exception message does not match the expected message in a test?

The assertion fails, and the test reports a failure showing the expected and actual messages, helping to identify the mismatch.

beginner

Show a simple JUnit 5 test snippet that checks for IllegalArgumentException with message "Invalid input".

@Test<br>void testInvalidInput() {<br>  IllegalArgumentException ex = assertThrows(IllegalArgumentException.class, () -> {<br>    methodThatThrows();<br>  });<br>  assertEquals("Invalid input", ex.getMessage());<br>}

Which JUnit method is used to check that a specific exception is thrown?

A assertThrows

B assertEquals

C assertTrue

D assertNull

assertThrows is designed to check that a block of code throws a specific exception.

How do you access the message of an exception in JUnit tests?

A exception.toString()

B exception.message()

C exception.getMessage()

D exception.getError()

The getMessage() method returns the detail message string of the exception.

Why should you check the exception message in addition to the exception type?

A To make tests run faster

B To confirm the exact error reason

C To avoid catching exceptions

D To ignore error details

Checking the message confirms the specific cause of the error, not just its type.

What happens if the exception message does not match the expected message in a test?

A The test fails

B The test passes

C The exception is ignored

D The test is skipped

A mismatch in messages causes the assertion to fail, marking the test as failed.

Which of these is a correct way to check exception message in JUnit 5?

A assertTrue(method().throwsException());

B assertThrows(Exception.class, () -> method(), "msg");

C assertEquals("msg", method().getMessage());

D Exception e = assertThrows(Exception.class, () -> method()); assertEquals("msg", e.getMessage());

You capture the exception with assertThrows, then check its message with getMessage().

Explain how to write a JUnit test that verifies both the type and message of an exception.

Think about how to capture and check exception details step by step.

Why is checking the exception message important in software testing?

Consider what information the message provides beyond the exception type.