Legacy code end-to-end test simplified example

MockitoExtensions.java

package com.jpragma.jtest;

import org.mockito.Mockito;
import org.mockito.stubbing.Answer;

import java.util.Arrays;

public class MockitoExtensions {
    private static Answer<?> alwaysThrowingAnswer = (invocation -> {
        throw new IllegalArgumentException("Unexpected call to " + invocation.getMethod() +
                " with " + Arrays.toString(invocation.getArguments()));
    });

    public static <T> T strictMock(Class<T> clazz) {
        return Mockito.mock(clazz, alwaysThrowingAnswer);
    }
}

XyzComponentIT.java

package com.jpragma.jtest.xyz;

import com.jpragma.jtest.MockitoExtensions;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.TestConfiguration;
import org.springframework.context.annotation.Bean;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit.jupiter.SpringExtension;

import static org.mockito.ArgumentMatchers.any;
import static org.mockito.Mockito.*;

@ExtendWith(SpringExtension.class)
@ContextConfiguration(classes = XyzComponentIT.Config.class)
public class XyzComponentIT {

    @Autowired
    XyzController controller;
    @Autowired
    AddressValidator addressValidator;
    @Autowired
    CustomerRepository customerRepository;
    @Autowired
    EmailServiceClient emailServiceClient;

    @Test
    void updateCustomerProfile() {
        CustomerProfile customerProfile = new CustomerProfile()
                .setId("001")
                .setFirstName("John")
                .setLastName("Doe")
                .setAddress(
                        new PrimaryAddress()
                                .setStreet("1 Main st")
                                .setCity("Toronto")
                                .setRegion("ON")
                                .setCountry("Canada")
                );

        doReturn(true).when(addressValidator).validateAddress(any(PrimaryAddress.class));
        doNothing().when(customerRepository).persistProfile(any(CustomerProfile.class));
        String email = "jdoe@email.com";
        doReturn(email).when(customerRepository).getCustomerEmail(customerProfile.getId());
        doNothing().when(emailServiceClient).sendEmail(anyString(), anyString());

        controller.updateCustomerProfile(customerProfile);

        verify(customerRepository).persistProfile(customerProfile);
        verify(emailServiceClient).sendEmail(email, "Profile Update");
    }

    @TestConfiguration
    static class Config {
        @Bean
        XyzController controller() {
            return new XyzController(profileUpdateService());
        }
        @Bean
        ProfileUpdateService profileUpdateService() {
            return new ProfileUpdateServiceImpl(addressValidator(), customerRepository(), emailServiceClient());
        }
        @Bean
        AddressValidator addressValidator() {
            return MockitoExtensions.strictMock(AddressValidator.class);
        }
        @Bean
        CustomerRepository customerRepository() {
            return MockitoExtensions.strictMock(CustomerRepository.class);
        }
        @Bean
        EmailServiceClient emailServiceClient() {
            return MockitoExtensions.strictMock(EmailServiceClient.class);
        }
    }
}