assertThrows usage 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

BIndexOutOfBoundsException

CArithmeticException

DNullPointerException

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong exception class.

Not using the .class suffix.

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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ANullPointerException

BNumberFormatException

CArithmeticException

DIllegalStateException

Attempts:

3 left

💡 Hint

Common Mistakes

Using NullPointerException instead of ArithmeticException.

Forgetting to use .class after the exception name.

Dividing by zero throws an ArithmeticException, so that is the correct exception to assert.

3fill in blank

hard

Fix the error in the assertThrows usage to correctly check for IndexOutOfBoundsException.

JUnit

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

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AIndexOutOfBoundsException()

BIndexOutOfBoundsException.class

Cnew IndexOutOfBoundsException()

DIndexOutOfBoundsException

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the exception class name without .class.

Passing a new exception instance instead of the class.

The assertThrows method requires the exception class literal, which is IndexOutOfBoundsException.class. Passing the class name without .class or an instance causes errors.

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.

Using the wrong exception class.

The code should assert NumberFormatException.class and parse the invalid string "abc" which causes the exception.

5fill in blank

hard

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

JUnit

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

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AIllegalArgumentException

B"Invalid input"

DNullPointerException

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different exception class.

Mismatching the exception message string.

The test asserts that IllegalArgumentException.class is thrown with the message "Invalid input". The message is passed to the exception and checked with assertEquals.