Creating custom AssertJ assertions

In this recipe, we will create a custom AssertJ assertion. Please refer to the previous recipe for the presented assertions in the test because in the current recipe, we will combine them into our custom assertions:

Getting ready

For this recipe, our system under test will be a NewPersonGenerator class that will call an external service, NewIdentityCreator, to generate a new identity for the current person, as shown in the following code:

public class NewPersonGenerator {

    private final NewIdentityCreator newIdentityCreator;

    public NewPersonGenerator(NewIdentityCreator newIdentityCreator) {
        this.newIdentityCreator = newIdentityCreator;
    }

    public Person generateNewIdentity(Person person) {
        String newName = newIdentityCreator.createNewName(person);
        int newAge = newIdentityCreator.createNewAge(person);
        List<Person> newSiblings = newIdentityCreator.createNewSiblings(person);
        return new Person(newName...