The purpose of this post is simply to give a hint on how to use Mockito, Spy, and JUnit 5.

package se.tkartor.microservice.tols;

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.Mock;
import org.mockito.Mockito;
import org.mockito.junit.jupiter.MockitoExtension;

@ExtendWith(MockitoExtension.class)
public class MockTest {

    @Mock
    Car mockCarTWO;

    @Test
    public void noMockJustAssertTest() {
        Car car = new Car("red", 250, new Wheels(19));
        Assertions.assertEquals(250, car.maxSpeed);
    }

    /**
     * The purpose of this test is to show that a Mock can be created
     * using the API and does not have to be created using the @Mock annotation
     * NOTE! that creating a mock out of a class, means that it still serves
     * the interface/API of the original class, but NONE of the methods
     * will do anything nor will the return anything
     * The mock-instance is simply an empty shell, and hence the last
     * commented-out code/line is not possible, since it will return NULL
     */
    @Test
    public void mockitoAPItest() {
        Car mockCar = Mockito.mock(Car.class);
        mockCar.setColor("blue");
        mockCar.setMaxSpeed(100);
        Mockito.verify(mockCar).setColor("blue");
        // Assertions.assertEquals("blue" , mockCar.getColor());
        Assertions.assertNull( mockCar.getColor() );
    }

    /**
     * Based on the fact that a mocked class is an empty shell
     * it is possible to also attach a.k.a spy on a instance
     * and carry out mocking this way, this is useful when you have
     * and instance that does everything right, except you need to
     * see what happens when you demand it to return a certain value
     * under certain cirumstances. The example below hopefully
     * explains this :-)
     */
    @Test
    public void spyTest() {
        Car mockCar = Mockito.spy(new Car("red", 90, new Wheels(19)));
        mockCar.setColor("blue");
        mockCar.setMaxSpeed(100);
        Mockito.verify(mockCar).setColor("blue");
        Assertions.assertEquals("blue", mockCar.getColor());
    }

    /**
     * Nothing new, as explained above
     * the instance of the mocked class will be an empty shell
     */
    @Test
    public void mockitoAPITest() {
        Car mockCar = Mockito.mock(Car.class);
        Mockito.when(mockCar.getColor()).thenReturn("green");
        mockCar.setColor("blue");
        mockCar.setMaxSpeed(100);
        mockCar.setWheels(new Wheels(19)); // this is possible since the api signature is there and hence the mock
        // allows it to be called, but it does not do anything
        Mockito.verify(mockCar).setColor("blue");
        Assertions.assertEquals("green", mockCar.getColor());
        Assertions.assertNull(mockCar.getWheels()); // This is null, since there is no mock for it
    }

    /**
     * The purpose with this test was simply
     * to use the @Mock annotation insead of the
     * mockito API, a somewhat lightweight / easy to read approach
     */
    @Test
    public void mockitoAnnotationTest() {
        Mockito.when(mockCarTWO.getColor()).thenReturn("green");
        Assertions.assertEquals("green", mockCarTWO.getColor());
    }

    public static class Wheels {
        private int size;

        public Wheels(int size) {
            this.size = size;
        }

        public int getSize() {
            return size;
        }

        public void setSize(int size) {
            this.size = size;
        }
    }

    public static class Car {
        private String color;
        private long maxSpeed;
        private Wheels wheels;

        public Car(String color, long maxSpeed, Wheels wheels) {
            this.color = color;
            this.maxSpeed = maxSpeed;
            this.wheels = wheels;
        }

        public int wheelSize() {
            return wheels.getSize();
        }

        public String getColor() {
            return color;
        }

        public void setColor(String color) {
            this.color = color;
        }

        public long getMaxSpeed() {
            return maxSpeed;
        }

        public void setMaxSpeed(long maxSpeed) {
            this.maxSpeed = maxSpeed;
        }

        public Wheels getWheels() {
            return wheels;
        }

        public void setWheels(Wheels wheels) {
            this.wheels = wheels;
        }
    }
}