@Test annotation in JUnit - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple JUnit test with @Test

What will be the result of running this JUnit test class?

JUnit

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

public class SampleTest {
    @Test
    void testSum() {
        assertEquals(5, 2 + 3);
    }
}

A Compilation error due to missing main method.

B Test fails with an AssertionError.

C Test passes successfully with no errors.

D Runtime exception due to null pointer.

💡 Hint

Remember that @Test marks a method as a test and assertEquals checks expected vs actual values.

The testSum method checks if 2 + 3 equals 5. Since it does, the assertion passes and the test passes without errors.

❓ assertion

intermediate

Identify the failing assertion in a JUnit test

Given this test method, which assertion will cause the test to fail?

JUnit

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

public class AssertionTest {
    @Test
    void testValues() {
        assertTrue(3 > 2);
        assertFalse(5 < 1);
        assertEquals("hello", "hello");
        assertNotNull(null);
    }
}

A assertNotNull(null);

B assertFalse(5 < 1);

C assertEquals("hello", "hello");

D assertTrue(3 > 2);

💡 Hint

Check which assertion conditions are false or invalid.

assertNotNull(null) fails because the argument is null, so the assertion fails and the test fails at that point.

🧠 Conceptual

advanced

Purpose of the @Test annotation in JUnit

What is the main purpose of the @Test annotation in a JUnit test class?

A To ignore a test method during execution.

B To specify the order in which tests should run.

C To provide setup code before each test method.

D To mark a method as a test method that JUnit should run.

💡 Hint

Think about how JUnit knows which methods to execute as tests.

The @Test annotation tells JUnit that the method is a test method to be executed during testing.

🔧 Debug

advanced

Identify the error in this JUnit test method

What error will occur when running this test class?

JUnit

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

public class DebugTest {
    @Test
    void testDivision() {
        int result = 10 / 0;
        assertEquals(0, result);
    }
}

A Compilation error due to division by zero.

B ArithmeticException: division by zero at runtime.

C AssertionError because result is not zero.

D Test passes successfully.

💡 Hint

Division by zero is not allowed in Java and causes an exception.

The code divides 10 by 0, which causes an ArithmeticException at runtime before the assertion is reached.

❓ framework

expert

Behavior of @Test with expected exception in JUnit 5

Consider this test method in JUnit 5. What is the test result?

JUnit

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

public class ExceptionTest {
    @Test
    void testException() {
        assertThrows(IllegalArgumentException.class, () -> {
            throw new IllegalArgumentException("Invalid argument");
        });
    }
}

A Test passes because the expected exception is thrown.

B Test fails because no exception is thrown.

C Test fails due to a compilation error in assertThrows usage.

D Test fails because a different exception is thrown.

💡 Hint

assertThrows expects the specified exception to be thrown inside the lambda.

The lambda throws IllegalArgumentException as expected, so assertThrows passes and the test passes.