Checking exception type hierarchy in JUnit - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to assert that the method throws an IOException.

JUnit

assertThrows([1].class, () -> methodThatThrows());

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ARuntimeException

BError

CException

DIOException

Attempts:

3 left

💡 Hint

Common Mistakes

Using a superclass like Exception instead of the specific IOException.

Using an unrelated exception type like RuntimeException.

The method is expected to throw an IOException, so we assertThrows with IOException.class.

2fill in blank

medium

Complete the code to assert that the method throws a NullPointerException.

JUnit

assertThrows([1].class, () -> methodThatThrowsNull());

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ANullPointerException

BIOException

CIllegalArgumentException

DIndexOutOfBoundsException

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing NullPointerException with IllegalArgumentException.

Using a superclass Exception instead of the specific exception.

The method throws a NullPointerException, so we assertThrows with NullPointerException.class.

3fill in blank

hard

Fix the error in the assertion to check for the correct exception type.

JUnit

assertThrows([1].class, () -> methodThatThrows());

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AIOException

BException

CFileNotFoundException

DRuntimeException

Attempts:

3 left

💡 Hint

Common Mistakes

Using a superclass Exception which is too general.

Using a subclass FileNotFoundException which may not be thrown.

The method throws IOException, so the assertion must check for IOException.class, not a superclass or subclass.

4fill in blank

hard

Fill both blanks to assert that the method throws an IllegalArgumentException with the expected message.

JUnit

IllegalArgumentException thrown = assertThrows([1].class, () -> methodThatThrowsIllegal());
assertTrue(thrown.getMessage().[2]("Invalid argument"));

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AIllegalArgumentException

Bcontains

CstartsWith

DendsWith

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong exception class like RuntimeException.

Using startsWith or endsWith which may fail if message format changes.

We assertThrows with IllegalArgumentException.class and check that the message contains "Invalid argument" using contains().

5fill in blank

hard

Fill all three blanks to assert that the method throws a custom exception and check its cause and message.

JUnit

CustomException ex = assertThrows([1].class, () -> methodThatThrowsCustom());
assertNotNull(ex.getCause());
assertEquals("[2]", ex.getCause().getClass().getSimpleName());
assertTrue(ex.getMessage().[3]("custom error"));

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ACustomException

BIOException

Ccontains

DstartsWith

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong exception class in assertThrows.

Checking cause with incorrect class name.

Using startsWith instead of contains for message check.

We assertThrows with CustomException.class, check that the cause is an IOException, and verify the message contains "custom error".