Injecting test doubles instead of beans using Spring's code configuration

In this recipe, we will replace an existing bean with a test double using Spring's code configuration.

Getting ready

Let's assume that our system under test is the tax transferring system for a given person, as shown in the following code:

public class TaxTransferer {

    private final TaxService taxService;

    public TaxTransferer(TaxService taxService) {
        this.taxService = taxService;
    }

    public boolean transferTaxFor(Person person) {
        if (person == null) {
            return false;
        }
        taxService.transferTaxFor(person);
        return true;
    }

}

Where TaxService is a class that makes the web service call, as shown in the following code (for simplicity, we are only writing that we are performing such data exchange):

class TaxService {

    public void transferTaxFor(Person person) {
        System.out.printf("Calling external web service for person with name [%s]%n", person.getName...