Verifying the order of interactions

In this recipe, we will verify that a set of methods get executed in the specified order.

Getting ready

For this recipe, our system under test will be TaxUpdator which is a simplified version of a facade that calls the TaxService methods (let's assume that it is a web service) to update tax-related data and perform a series of tax transfers. Let's assume that this web service is a legacy, a badly-written system, and we have to synchronously call it in a precisely defined sequence.

Let's take a look at the implementation of the TaxUpdator class:

public class TaxUpdator {

    public static final int TAX_FACTOR = 100;

    private final TaxService taxService;

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

    public void transferTaxFor(Person person) {
        taxService.updateTaxFactor(person, calculateTaxFactor(1));
        taxService.transferTaxFor(person);
        taxService.transferTaxFor(person);
        taxService...