DependencyOverrideExampleTests.java

import static org.mockito.Mockito.*;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.Spy;
import org.mockito.runners.MockitoJUnitRunner;

@RunWith(MockitoJUnitRunner.class)
public class DependencyOverrideExampleTests {

	@Spy Component component = new Component(new DependencyA());

	@Test
	public void runWithDepenencyA() {
		component.someLogic();
	}

	@Test
	public void runWithDepenencyB() {

		when(component.getDependency()).thenReturn(new DependencyB());

		component.someLogic();
	}
}

interface Dependency {}

class DependencyA implements Dependency {}

class DependencyB implements Dependency {}

class Component {

	private final Dependency dependency;

	public Component(Dependency dependency) {
		this.dependency = dependency;
	}

	public Dependency getDependency() {
		return dependency;
	}

	public void someLogic() {
		System.out.println("using dependency: " + getDependency());
	}
}