assertThrows for exceptions in JUnit - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to assert that a NullPointerException is thrown.

JUnit

assertThrows([1].class, () -> { throw new NullPointerException(); });

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AIllegalArgumentException

BIOException

CNullPointerException

DRuntimeException

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different exception class than the one thrown.

Forgetting to add .class after the exception name.

The assertThrows method expects the exception class that should be thrown. Here, NullPointerException.class is correct.

2fill in blank

medium

Complete the code to assert that an ArithmeticException is thrown when dividing by zero.

JUnit

assertThrows([1].class, () -> { int result = 10 / 0; });

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AIllegalStateException

BNullPointerException

CArrayIndexOutOfBoundsException

DArithmeticException

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong exception class like NullPointerException.

Not matching the exception type thrown by the code.

Dividing by zero throws an ArithmeticException, so assertThrows should expect ArithmeticException.class.

3fill in blank

hard

Fix the error in the code to correctly assert that an IndexOutOfBoundsException is thrown.

JUnit

assertThrows([1].class, () -> { List<String> list = new ArrayList<>(); list.get(1); });

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AIndexOutOfBoundsException

BIllegalArgumentException

CNullPointerException

DIOException

Attempts:

3 left

💡 Hint

Common Mistakes

Using NullPointerException instead of IndexOutOfBoundsException.

Forgetting to specify the correct exception class.

Accessing an invalid index in a list throws IndexOutOfBoundsException, so assertThrows should expect IndexOutOfBoundsException.class.

4fill in blank

hard

Fill both blanks to assert that a NumberFormatException is thrown when parsing an invalid number.

JUnit

assertThrows([1].class, () -> { Integer.parseInt([2]); });

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ANumberFormatException

B"abc"

C"123"

DIllegalArgumentException

Attempts:

3 left

💡 Hint

Common Mistakes

Using a valid number string like "123" which does not throw exception.

Using the wrong exception class.

Parsing "abc" as an integer throws NumberFormatException, so the first blank is NumberFormatException.class and the second blank is the invalid string "abc".

5fill in blank

hard

Fill all three blanks to assert that an IllegalArgumentException is thrown with a custom message.

JUnit

IllegalArgumentException exception = assertThrows([1].class, () -> { throw new [2]([3]); });
assertEquals("Invalid input", exception.getMessage());

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AIllegalArgumentException

C"Invalid input"

D"Error"

Attempts:

3 left

💡 Hint

Common Mistakes

Using different exception classes in assertThrows and throw statement.

Passing a wrong message string that does not match the assertion.

To assert the exception and check its message, use IllegalArgumentException.class for the first blank, throw new IllegalArgumentException for the second, and pass the message "Invalid input" as the third.