Chained and combined assertions

AssertJ's fluent API lets you chain multiple assertions on the same object, and combine checks for multiple elements into a single statement. This makes tests more concise, more readable, and produces better failure messages.

Chain assertions on the same object

Having many separate assertThat() calls on the same object decreases readability. Chain them instead.

Before

ChainedAssertJTest.java

import java.util.List;

class ChainedAssertJTest {

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

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

warning

The long list of separate assertions makes the test longer and harder to read.

After

ChainedAssertJTest.java

import org.junit.jupiter.api.Test;

import java.util.List;

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

class ChainedAssertJTest {

    @Test
    void bundle() {
        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));

        // Or even shorter:
        assertThat(books)
                .containsExactly(
                        new Book("Effective Java", "Joshua Bloch", 2001),
                        new Book("Java Concurrency in Practice", "Brian Goetz", 2006),
                        new Book("Clean Code", "Robert C. Martin", 2008));
    }
}

tip

Using chained assertions makes the test more fluent and easier to read.

Combine checks for multiple elements

When checking for multiple elements, pass them all to a single assertion instead of repeating assertTrue().

Before

AssertListContains.java

import org.junit.jupiter.api.Test;

import java.util.List;

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

class AssertListContains {

    List<String> list = List.of("a", "b", "c");

    @Test
    void assertMultipleElements() {
        assertTrue(list.contains("a"));
        assertTrue(list.contains("b"));
        assertTrue(list.contains("c"));
    }
}

warning

Multiple assertTrue() calls are verbose and stop at the first failure, hiding subsequent issues.

After

AssertListContains.java

import org.junit.jupiter.api.Test;

import java.util.List;

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

class AssertListContains {

    List<String> list = List.of("a", "b", "c");

    @Test
    void assertMultipleElements() {
        assertThat(list).contains("a", "b", "c");
    }
}

tip

AssertJ allows checking for multiple elements in a single assertion, making the test more concise and showing all missing elements in case of failure.