How do you Test Getter and Setter Interface in Java using Mockito (Mocking)?

Usually, we unit tests the logics. An interface is without implementation details. A interface is just a binding a contract, but still, we can use Mockito to mock the interface, and test it.

For example, given the following simple Setter and Getter Interface:

interface GetAndSet {
    void setValue(String name);
    String getValue();
}

We can test it like this – thanks to the Mockito mocking framework in Java. We use doAnswer method to intercept the invokation of a interface method i.e. setter, then at the time, we mock the getter.

package com.helloacm;

import lombok.val;
import org.junit.jupiter.api.Test;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.mockito.Mockito.*;

interface GetAndSet {
    void setValue(String name);
    String getValue();
}

public class ExampleTest {
    @Test
    public void test_simple_getter_setter_interface() {
        val instance = mock(GetAndSet.class);

        doAnswer(invocation -> {
            // or use invocation.getArgument(0);
            val name = (String)invocation.getArguments()[0];
            when(instance.getValue()).thenReturn(name);
            return null;
        }).when(instance).setValue(anyString());

        instance.setValue("HelloACM.com");
        assertEquals("HelloACM.com", instance.getValue());
    }
}

If the method we are mocking is not void – we can use when. For example:

when(instance.getValue()).thenAnswer(innocation -> {
     return "Hello";
});

–EOF (The Ultimate Computing & Technology Blog) —