@BeforeEach method in JUnit - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of @BeforeEach initialization

Consider the following JUnit 5 test class. What will be the output when the test method runs?

JUnit

import org.junit.jupiter.api.*;

public class SampleTest {
    private int counter = 0;

    @BeforeEach
    void setup() {
        counter += 5;
        System.out.println("Setup called. Counter = " + counter);
    }

    @Test
    void testCounter() {
        System.out.println("Test running. Counter = " + counter);
        Assertions.assertEquals(5, counter);
    }
}

A

Setup called. Counter = 0
Test running. Counter = 0

B

Setup called. Counter = 10
Test running. Counter = 10

C

Setup called. Counter = 5
Test running. Counter = 5

D

Setup called. Counter = 5
Test running. Counter = 10

💡 Hint

Remember that @BeforeEach runs before every test method and the instance is recreated for each test.

The @BeforeEach method runs before each test method. Since the test class instance is recreated for each test, the counter starts at 0 each time. The setup method adds 5, so the counter is 5 when the test runs.

❓ assertion

intermediate

Correct assertion to verify @BeforeEach effect

Given a @BeforeEach method that sets a list to contain exactly 3 elements before each test, which assertion correctly verifies this in a test method?

JUnit

import org.junit.jupiter.api.*;
import java.util.*;

public class ListTest {
    private List<String> items;

    @BeforeEach
    void setup() {
        items = new ArrayList<>();
        items.add("A");
        items.add("B");
        items.add("C");
    }

    @Test
    void testListSize() {
        // Which assertion is correct here?
    }
}

A Assertions.assertEquals(3, items.size());

B Assertions.assertTrue(items.isEmpty());

C Assertions.assertNull(items);

D Assertions.assertEquals(0, items.size());

💡 Hint

Check the size of the list after @BeforeEach runs.

The @BeforeEach method initializes the list with 3 elements. So the list size should be 3. Option A correctly asserts this.

🔧 Debug

advanced

Why does the test fail despite @BeforeEach initialization?

Examine the code below. The test fails with a NullPointerException. What is the most likely cause?

JUnit

import org.junit.jupiter.api.*;
import java.util.*;

public class NullTest {
    private List<String> items;

    @BeforeEach
    void setup() {
        List<String> items = new ArrayList<>();
        items.add("X");
    }

    @Test
    void testNotNull() {
        Assertions.assertEquals(1, items.size());
    }
}

A The items list is cleared after setup, causing NullPointerException.

B The @BeforeEach annotation is missing, so setup is not called.

C The test method runs before the setup method.

D The setup method declares a new local variable 'items' instead of initializing the instance variable.

💡 Hint

Check variable scope inside the setup method.

The setup method declares a new local variable 'items' which shadows the instance variable. The instance variable remains null, causing NullPointerException in the test.

🧠 Conceptual

advanced

Behavior of @BeforeEach with static variables

If a static variable is modified inside a @BeforeEach method, what is the expected behavior across multiple test methods in the same class?

A The static variable causes tests to run in parallel automatically.

B The static variable retains its modified value across all test methods.

C The static variable is reinitialized by JUnit before each test method.

D The static variable is reset to default before each test method automatically.

💡 Hint

Static variables belong to the class, not instances.

Static variables are shared across all instances of the class. Modifying them in @BeforeEach affects all tests because the variable is not reset automatically.

❓ framework

expert

Order of execution with multiple lifecycle annotations

Given the following JUnit 5 test class, what is the correct order of printed output when the single test runs?

JUnit

import org.junit.jupiter.api.*;

public class LifecycleTest {

    @BeforeAll
    static void beforeAll() {
        System.out.println("BeforeAll");
    }

    @BeforeEach
    void beforeEach() {
        System.out.println("BeforeEach");
    }

    @Test
    void test() {
        System.out.println("Test");
    }

    @AfterEach
    void afterEach() {
        System.out.println("AfterEach");
    }

    @AfterAll
    static void afterAll() {
        System.out.println("AfterAll");
    }
}

A

BeforeAll
BeforeEach
Test
AfterEach
AfterAll

B

BeforeEach
BeforeAll
Test
AfterEach
AfterAll

C

BeforeAll
Test
BeforeEach
AfterEach
AfterAll

D

BeforeAll
BeforeEach
AfterEach
Test
AfterAll

💡 Hint

Remember the order: BeforeAll once, BeforeEach before each test, AfterEach after each test, AfterAll once.

JUnit 5 runs lifecycle methods in this order: @BeforeAll (once), @BeforeEach (before each test), @Test, @AfterEach (after each test), @AfterAll (once).