JUnit 4 vs JUnit 5 (Jupiter) differences

Introduction

JUnit 4 and JUnit 5 are versions of a tool that helps test Java code. Knowing their differences helps you write better tests and use the right features.

When starting a new Java project and choosing a testing framework.

When updating old tests to use newer features and better structure.

When needing better support for modern Java features like lambdas.

When wanting more flexible and powerful test lifecycle controls.

When integrating tests with modern build tools and IDEs.

Syntax

JUnit

JUnit 4 example:

import org.junit.Test;
import static org.junit.Assert.*;

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

JUnit 5 example:

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

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

JUnit 5 uses the package org.junit.jupiter.api instead of org.junit.

JUnit 5 test methods can have default (package-private) visibility, no need to be public.

Examples

JUnit 4 test method must be public and annotated with @Test.

JUnit

@Test
public void testMethod() {
    assertTrue(true);
}

JUnit 5 test method can be package-private (no modifier) and uses @Test from Jupiter.

JUnit

@Test
void testMethod() {
    assertTrue(true);
}

JUnit 4 uses @Before for setup before each test.

JUnit

@Before
public void setup() {
    // runs before each test in JUnit 4
}

JUnit 5 uses @BeforeEach instead of @Before.

JUnit

@BeforeEach
void setup() {
    // runs before each test in JUnit 5
}

Sample Program

This JUnit 5 test class has two simple tests for addition and subtraction. Each test checks if the math result is correct.

JUnit

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

public class CalculatorTest {

    @Test
    void additionTest() {
        int result = 2 + 3;
        assertEquals(5, result, "2 + 3 should equal 5");
    }

    @Test
    void subtractionTest() {
        int result = 5 - 3;
        assertEquals(2, result, "5 - 3 should equal 2");
    }
}

Important Notes

JUnit 5 is modular and supports running JUnit 4 tests via a vintage engine.

JUnit 5 supports lambda expressions for assertions, making tests cleaner.

JUnit 5 has better support for tagging and filtering tests.

Summary

JUnit 5 is the newer, more flexible version of JUnit with better Java support.

JUnit 4 requires public test methods; JUnit 5 does not.

Annotations like @Before in JUnit 4 are replaced by @BeforeEach in JUnit 5.

Practice

1. Which of the following is a key difference between JUnit 4 and JUnit 5 regarding test method visibility?

easy

A. JUnit 4 requires test methods to be public, but JUnit 5 does not.

B. JUnit 5 requires test methods to be public, but JUnit 4 does not.

C. Both JUnit 4 and JUnit 5 require test methods to be private.

D. Neither JUnit 4 nor JUnit 5 require any specific visibility for test methods.

Solution

1. Step 1: Understand JUnit 4 test method visibility

   JUnit 4 requires test methods to be declared as public for the framework to recognize and run them.

2. Step 2: Understand JUnit 5 test method visibility

   JUnit 5 allows test methods to have any visibility, including package-private, making it more flexible.

3. Final Answer:

   JUnit 4 requires test methods to be public, but JUnit 5 does not. -> Option A

4. Quick Check:

   JUnit 4 public test methods = true [OK]

Hint: Remember: JUnit 4 needs public tests; JUnit 5 is more relaxed [OK]

Common Mistakes:

• Thinking JUnit 5 also requires public test methods
• Assuming both versions have the same visibility rules
• Confusing private and public requirements

2. Which annotation replaces @Before from JUnit 4 in JUnit 5?

easy

A. @Init

B. @BeforeAll

C. @Setup

D. @BeforeEach

Solution

1. Step 1: Identify JUnit 4 setup annotation

   JUnit 4 uses @Before to run code before each test method.

2. Step 2: Identify JUnit 5 equivalent annotation

   JUnit 5 replaces @Before with @BeforeEach to clarify it runs before each test method.

3. Final Answer:

   @BeforeEach -> Option D

4. Quick Check:

   @Before in JUnit 4 = @BeforeEach in JUnit 5 [OK]

Hint: Think "Each" means before every test, replacing @Before [OK]

Common Mistakes:

• Choosing @BeforeAll which runs once before all tests
• Using non-existent annotations like @Setup or @Init
• Confusing @BeforeEach with @AfterEach

3. Consider this JUnit 5 test class snippet:

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

class CalculatorTest {
  @Test
  void addTest() {
    int result = 2 + 3;
    assertEquals(5, result);
  }
}

What will be the test result when running this test?

medium

A. Test passes successfully

B. Test fails with assertion error

C. Compilation error due to missing public modifier

D. Runtime error due to missing @BeforeEach

Solution

1. Step 1: Check method visibility in JUnit 5

   The test method is package-private (no modifier), which is allowed in JUnit 5.

2. Step 2: Verify assertion correctness

   The assertion compares 5 and result (2+3=5), so it matches and passes.

3. Final Answer:

   Test passes successfully -> Option A

4. Quick Check:

   2 + 3 = 5, assertion true [OK]

Hint: JUnit 5 allows non-public tests; 2+3=5 means pass [OK]

Common Mistakes:

• Assuming test methods must be public in JUnit 5
• Thinking missing @BeforeEach causes failure here
• Confusing assertion order causing failure

4. Given this JUnit 4 test snippet:

import org.junit.Before;
import org.junit.Test;

public class SampleTest {
  @Before
  public void setup() {
    System.out.println("Setup");
  }

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

What is the main issue when running this test?

medium

A. No issues; test runs and prints both lines

B. The test method must be public in JUnit 4

C. The setup method must be static

D. The @Before annotation is not recognized in JUnit 4

Solution

1. Step 1: Check test method visibility requirement in JUnit 4

   JUnit 4 requires test methods to be public, but here testMethod() has default (package-private) visibility.

2. Step 2: Verify @Before method correctness

   The setup() method is public and correctly annotated, so no issue there.

3. Final Answer:

   The test method must be public in JUnit 4 -> Option B

4. Quick Check:

   JUnit 4 test methods must be public [OK]

Hint: JUnit 4 needs public test methods; check method modifiers [OK]

Common Mistakes:

• Thinking @Before is invalid in JUnit 4
• Assuming setup must be static
• Believing test runs despite non-public test method

5. You want to migrate a JUnit 4 test class to JUnit 5. Which of these changes is NOT required?

hard

A. Change import statements to JUnit Jupiter packages

B. Replace @Before with @BeforeEach

C. Make all test methods public

D. Replace @Test import to JUnit Jupiter's @Test

Solution

1. Step 1: Identify visibility requirements in JUnit 5

   JUnit 5 does not require test methods to be public; package-private is allowed.

2. Step 2: Check other migration steps

   Replacing @Before with @BeforeEach and updating imports to Jupiter packages are required for migration.

3. Final Answer:

   Make all test methods public -> Option C

4. Quick Check:

   JUnit 5 relaxes method visibility rules [OK]

Hint: JUnit 5 allows non-public tests; no need to change visibility [OK]

Common Mistakes:

• Thinking test methods must be public in JUnit 5
• Forgetting to update import statements
• Missing @Before to @BeforeEach replacement