Why exception testing validates error handling in JUnit - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the method throws the expected exception.

JUnit

assertThrows([1].class, () -> calculator.divide(10, 0));

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AIllegalArgumentException

BNullPointerException

CIOException

DArithmeticException

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong exception type like NullPointerException.

Not using the exception class with .class suffix.

The ArithmeticException is expected when dividing by zero.

2fill in blank

medium

Complete the code to verify the exception message contains the expected text.

JUnit

Exception exception = assertThrows(IllegalArgumentException.class, () -> parser.parse(null));
assertTrue(exception.getMessage().[1]("input cannot be null"));

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Aequals

Bcontains

CstartsWith

DendsWith

Attempts:

3 left

💡 Hint

Common Mistakes

Using equals which requires exact match.

Using startsWith or endsWith which only check the start or end.

We use contains to check if the exception message includes the expected text.

3fill in blank

hard

Fix the error in the test code to properly catch the exception.

JUnit

try {
    service.process(null);
    fail("Expected [1] to be thrown");
} catch (NullPointerException e) {
    // test passes
}

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ANullPointerException

BIllegalStateException

CIOException

DRuntimeException

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatching exception type in fail message and catch block.

Using a generic exception type that is not thrown.

The test expects a NullPointerException when passing null to process.

4fill in blank

hard

Fill both blanks to assert that the method throws the correct exception with the expected message.

JUnit

IllegalArgumentException thrown = assertThrows([1].class, () -> validator.validate(""));
assertEquals("[2]", thrown.getMessage());

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AIllegalArgumentException

BNullPointerException

CInput cannot be empty

DValue is null

Attempts:

3 left

💡 Hint

Common Mistakes

Using NullPointerException instead of IllegalArgumentException.

Using wrong exception message text.

The method throws IllegalArgumentException with message "Input cannot be empty" when input is empty.

5fill in blank

hard

Fill all three blanks to test that the method throws the expected exception type, and the message contains the correct text.

JUnit

Exception exception = assertThrows([1].class, () -> fileReader.readFile(null));
String expectedMessage = "[2]";
assertTrue(exception.getMessage().[3](expectedMessage));

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AIllegalArgumentException

BFile path must not be null

Ccontains

DIOException

Attempts:

3 left

💡 Hint

Common Mistakes

Using IOException instead of IllegalArgumentException.

Checking message with equals instead of contains.

The test expects IllegalArgumentException with a message containing "File path must not be null".