Old Java versions

Java 13 introduced text blocks (multi-line strings) as a preview feature, finalized in Java 15. They make working with multi-line strings much more readable, but traditional string concatenation is still commonly found in older tests.

String concatenation

Traditional string concatenation with + operators for multi-line strings is hard to read and maintain. Each line needs explicit \n newline characters and quote escaping.

Before

TextBlockTest.java

import com.github.timtebeek.books.Bundle;
import org.junit.jupiter.api.Test;

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

class TextBlockTest {
    @Test
    void summary() {
        String summary = new Bundle().summary();
        assertEquals("Books:\n" +
                        "Effective Java by Joshua Bloch (2001)\n" +
                        "Java Concurrency in Practice by Brian Goetz (2006)\n" +
                        "Clean Code by Robert C. Martin (2008)\n" +
                        "Authors:\n" +
                        "Joshua Bloch\n" +
                        "Brian Goetz\n" +
                        "Robert C. Martin\n" +
                        "Total books: 3\n" +
                        "Total authors: 3\n",
                summary);
    }
}

warning

String concatenation with + is verbose and error-prone. Missing newlines, extra spaces, and quote escaping make it hard to see the actual content.

After

TextBlockTest.java

import com.github.timtebeek.books.Bundle;
import org.junit.jupiter.api.Test;

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

class TextBlockTest {
    @Test
    void summary() {
        String summary = new Bundle().summary();
        assertEquals("""
                Books:
                Effective Java by Joshua Bloch (2001)
                Java Concurrency in Practice by Brian Goetz (2006)
                Clean Code by Robert C. Martin (2008)
                Authors:
                Joshua Bloch
                Brian Goetz
                Robert C. Martin
                Total books: 3
                Total authors: 3
                """,
                summary);
    }
}

tip

Text blocks make multi-line strings much more readable. The content is exactly as it appears, without escape sequences or concatenation operators.

Even better with AssertJ

While text blocks improve readability, AssertJ can make multi-line string comparisons even clearer with better diff output.

Before

TextBlockTest.java

import com.github.timtebeek.books.Bundle;
import org.junit.jupiter.api.Test;

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

class TextBlockTest {
    @Test
    void summary() {
        String summary = new Bundle().summary();
        assertEquals("""
                Books:
                Effective Java by Joshua Bloch (2001)
                Java Concurrency in Practice by Brian Goetz (2006)
                Clean Code by Robert C. Martin (2008)
                Authors:
                Joshua Bloch
                Brian Goetz
                Robert C. Martin
                Total books: 3
                Total authors: 3
                """,
                summary);
    }
}

info

JUnit's assertEquals() works with text blocks, but the diff output for multi-line strings can be hard to read when tests fail.

After

TextBlockTest.java

import com.github.timtebeek.books.Bundle;
import org.junit.jupiter.api.Test;

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

class TextBlockTest {
    @Test
    void summary() {
        String summary = new Bundle().summary();
        assertThat(summary).isEqualToIgnoringWhitespace("""
                Books:
                Effective Java by Joshua Bloch (2001)
                Java Concurrency in Practice by Brian Goetz (2006)
                Clean Code by Robert C. Martin (2008)
                Authors:
                Joshua Bloch
                Brian Goetz
                Robert C. Martin
                Total books: 3
                Total authors: 3
                """);
    }
}

tip

AssertJ provides better diff output for multi-line strings and offers flexible comparison methods like isEqualToIgnoringWhitespace() for when exact whitespace doesn't matter.

SequencedCollection

Java 21 introduced SequencedCollection, SequencedSet, and SequencedMap interfaces that provide uniform access to first and last elements. Before Java 21, accessing the last element required verbose index calculations. AssertJ 3.25.0+ provides dedicated assertions for these collections.

Before

SequencedCollectionTest.java

import org.junit.jupiter.api.Test;

import java.util.List;

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

class SequencedCollectionTest {
    @Test
    void lastElement() {
        List<String> authors = List.of(
                "Joshua Bloch",
                "Brian Goetz",
                "Robert C. Martin"
        );
        assertThat(authors.get(authors.size() - 1)).isEqualTo("Robert C. Martin");
    }
}

warning

Accessing the last element with get(size() - 1) is verbose and requires mental overhead to understand the intent. It's also prone to off-by-one errors.

After

SequencedCollectionTest.java

import org.junit.jupiter.api.Test;

import java.util.List;

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

class SequencedCollectionTest {
    @Test
    void lastElement() {
        List<String> authors = List.of(
                "Joshua Bloch",
                "Brian Goetz",
                "Robert C. Martin"
        );
        assertThat(authors).last().isEqualTo("Robert C. Martin");
    }
}

tip

AssertJ's last() method is clear and expressive. It works with any SequencedCollection (including List, Deque, LinkedHashSet) and provides better failure messages. There's also a first() method for accessing the first element.

Adopting Java 21+ features in your tests

You can use OpenRewrite to automatically migrate your tests to use Java 21 features like text blocks and SequencedCollection assertions. See Java 21 for tests guide for detailed instructions on setting this up in your project.