Practice: Advanced AssertJ

Now it's your turn! Apply the advanced AssertJ techniques you've learned to improve the test code in the orders package.

Exercise: Order Collection Tests

Navigate to orders/src/test/java/com/github/timtebeek/orders/OrderServiceTest.java.

This test class works with a collection of orders and demonstrates several opportunities to use advanced AssertJ features.

Your tasks

1. Use extracting() - Replace manual stream mapping with method references to extract properties from collections
2. Use filteredOn() - Replace manual stream filtering with fluent filtering predicates
3. Use SoftAssertions - Group multiple assertions on the same object so all conditions are checked
4. Use flatExtracting() - Replace manual flatMap operations when working with nested collections

Solution

First try out the exercise yourself, then you can check out the solution below.

Click to see the refactored tests

OrderServiceTest.java

package com.github.timtebeek.orders;

import org.assertj.core.api.SoftAssertions;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;

import java.math.BigDecimal;
import java.time.LocalDate;
import java.util.List;

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

class OrderServiceTest {

    private List<Order> orders;

    @BeforeEach
    void setUp() {
        OrderItem item1 = new OrderItem("P1", "Laptop", "Electronics", 1,
          new BigDecimal("1000.00"), new BigDecimal("1000.00"));
        OrderItem item2 = new OrderItem("P2", "Mouse", "Electronics", 2,
          new BigDecimal("25.00"), new BigDecimal("50.00"));
        OrderItem item3 = new OrderItem("P3", "Keyboard", "Electronics", 1,
          new BigDecimal("75.00"), new BigDecimal("75.00"));

        orders = List.of(
          new Order("ORD-001", "CUST-001", LocalDate.of(2024, 1, 15), "PENDING",
            List.of(item1), new BigDecimal("1000.00"), new BigDecimal("85.00"),
            new BigDecimal("0.00"), new BigDecimal("50.00"), new BigDecimal("1035.00")),
          new Order("ORD-002", "CUST-002", LocalDate.of(2024, 1, 16), "CONFIRMED",
            List.of(item2, item3), new BigDecimal("125.00"), new BigDecimal("10.63"),
            new BigDecimal("9.99"), new BigDecimal("12.50"), new BigDecimal("133.12")),
          new Order("ORD-003", "CUST-001", LocalDate.of(2024, 1, 17), "SHIPPED",
            List.of(item1, item2), new BigDecimal("1050.00"), new BigDecimal("89.25"),
            new BigDecimal("0.00"), new BigDecimal("52.50"), new BigDecimal("1086.75"))
        );
    }

    @Test
    void extractingOrderIds() {
        // Refactored: Using extracting() instead of manual stream mapping
        assertThat(orders)
          .extracting(Order::getOrderId)
          .containsExactly("ORD-001", "ORD-002", "ORD-003");
    }

    @Test
    void filteringAndExtracting() {
        // Refactored: Using filteredOn() instead of manual stream filtering
        assertThat(orders)
          .filteredOn(order -> order.getCustomerId().equals("CUST-001"))
          .extracting(Order::getOrderId)
          .containsExactly("ORD-001", "ORD-003");
    }

    @Test
    void multipleAssertionsOnOrder() {
        // Refactored: Using soft assertions to group multiple checks
        Order order = orders.getFirst();

        SoftAssertions.assertSoftly(softly -> {
            softly.assertThat(order.getOrderId()).isEqualTo("ORD-001");
            softly.assertThat(order.getCustomerId()).isEqualTo("CUST-001");
            softly.assertThat(order.getStatus()).isEqualTo("PENDING");
            softly.assertThat(order.getSubtotal()).isEqualByComparingTo(new BigDecimal("1000.00"));
            softly.assertThat(order.getTotal()).isEqualByComparingTo(new BigDecimal("1035.00"));
            softly.assertThat(order.getItems()).hasSize(1);
        });
    }

    @Test
    void flatExtractingItems() {
        // Refactored: Using flatExtracting() instead of manual flatMap operations
        assertThat(orders)
          .flatExtracting(Order::getItems)
          .extracting(OrderItem::getProductName)
          .contains("Laptop", "Mouse", "Keyboard");
    }
}

Run the tests

cd orders
mvn test -Dtest=OrderServiceTest

Next Steps

Once you're comfortable with these advanced AssertJ features, check out the Practice: Custom Assertions to learn how to create domain-specific assertion classes for even more readable tests!