Nothing special here, same changes as formerly, but we are using people.isEmpty() instead of people.size() == 0 for even better legibility.

package chapter11;

import org.junit.jupiter.api.Test;

import java.util.Set;

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

public class ForEachTest {

    record Person(String name, int age) {
    }

    interface Agency {

        boolean isChaperoneRequired(Set<Person> people);

    }

    static class AgencyBefore implements Agency {

        public boolean isChaperoneRequired(Set<Person> people) {
            boolean required = true;
            if (people.isEmpty()) {
                required = false;
            } else {
                for (var person : people) {
                    if (person.age() >= 18) {
                        required = false;
                        break;
                    }
                }
            }
            return required;
        }
    }

    static class AgencyAfter implements Agency {

        public boolean isChaperoneRequired(Set<Person> people) {
            return !people.isEmpty() &&
                    people.stream()
                            .noneMatch(person -> person.age() >= 18);
        }
    }

    private static void commonAgencyTests(Agency agency) {
        assertAll(
                () -> assertTrue(agency.isChaperoneRequired(
                        Set.of(new Person("Jake", 12)))),
                () -> assertTrue(agency.isChaperoneRequired(
                        Set.of(new Person("Jake", 12), new Person("Pam", 14)))),
                () -> assertTrue(agency.isChaperoneRequired(
                        Set.of(new Person("Shiv", 8),
                                new Person("Sam", 9), new Person("Jill", 11)))),
                () -> assertFalse(agency.isChaperoneRequired(
                        Set.of(new Person("Jake", 12), new Person("Pam", 18)))),
                () -> assertFalse(agency.isChaperoneRequired(Set.of()))
        );
    }

    @Test
    void agencyBefore() {
        commonAgencyTests(new AgencyBefore());
    }

    @Test
    void agencyAfter() {
        commonAgencyTests(new AgencyAfter());
    }
}