JUnit 3

JUnit 3 was the dominant testing framework for Java for many years, but it has several limitations compared to modern alternatives. Tests must extend TestCase, method names must start with test, and the assertion library is limited and not very expressive.

Limited expressiveness

JUnit 3 only provides basic assertions like assertTrue, assertFalse, assertEquals, and assertNotNull. This makes tests verbose and harder to understand, especially when they fail.

Before

JUnitThreeTest.java

import java.util.List;

public class JUnitThreeTest extends junit.framework.TestCase {

    public void testBundle() {
        List<Book> books = new Bundle().getBooks();

        assertNotNull(books);
        assertEquals(3, books.size());
        assertTrue(books.contains(new Book("Effective Java", "Joshua Bloch", 2001)));
        assertTrue(books.contains(new Book("Java Concurrency in Practice", "Brian Goetz", 2006)));
        assertTrue(books.contains(new Book("Clean Code", "Robert C. Martin", 2008)));
        assertFalse(books.contains(new Book("Java 8 in Action", "Raoul-Gabriel Urma", 2014)));

        String expectedTitle = books.get(0).getTitle();
        assertNotNull("Title not null", expectedTitle);
        assertEquals("Title should match", "Effective Java", expectedTitle);
    }
}

warning

JUnit 3 tests require extending TestCase, limiting inheritance, and test methods must be public and start with test. The limited assertion library makes tests verbose and less readable.

After

JUnitThreeTest.java

import org.junit.jupiter.api.Test;

import java.util.List;

import static org.assertj.core.api.Assertions.assertThat;

class JUnitThreeTest {

    @Test
    void testBundle() {
        List<Book> books = new Bundle().getBooks();

        assertThat(books)
                .hasSize(3)
                .contains(
                        new Book("Effective Java", "Joshua Bloch", 2001),
                        new Book("Java Concurrency in Practice", "Brian Goetz", 2006),
                        new Book("Clean Code", "Robert C. Martin", 2008))
                .doesNotContain(new Book("Java 8 in Action", "Raoul-Gabriel Urma", 2014));

        assertThat(books.get(0).getTitle())
                .as("Title should match")
                .isEqualTo("Effective Java");
    }
}

tip

Modern testing frameworks like JUnit 5 use annotations instead of naming conventions, don't require extending base classes, and pair well with AssertJ for more expressive assertions.

Confusing boolean assertions

Overuse of assertTrue and assertFalse with complex conditions makes it hard to understand what is being tested. When tests fail, the error messages are not helpful.

Before

JUnitThreeTest.java

public class JUnitThreeTest extends junit.framework.TestCase {

    public void testThatFails() {
        List<Book> books = new Bundle().getBooks();

        assertTrue(books.size() == 2);
        assertTrue(books.size() <= 2);
        assertTrue(books.size() < 2);

        assertFalse(books.size() == 3);
        assertFalse(books.size() <= 3);
        assertFalse(books.size() >= 3);
    }
}

danger

Using assertTrue and assertFalse with complex conditions produces unhelpful failure messages. When assertTrue(books.size() == 2) fails, you only see "expected: true but was: false" instead of the actual size.

After

JUnitThreeTest.java

import org.junit.jupiter.api.Test;

import static org.assertj.core.api.Assertions.assertThat;

class JUnitThreeTest {

    @Test
    void testThatFails() {
        List<Book> books = new Bundle().getBooks();

        assertThat(books)
                .hasSize(2)
                .hasSizeLessThanOrEqualTo(2)
                .hasSizeLessThan(2);

        assertThat(books).doesNotHaveSize(3);
    }
}

tip

AssertJ provides dedicated assertion methods that produce clear, informative failure messages showing both expected and actual values.