Mockito Spys

MockitoSpyTest.java

import org.junit.Test;
import org.junit.runner.RunWith;

import static org.mockito.Mockito.*;

import org.mockito.runners.MockitoJUnitRunner;

@RunWith(MockitoJUnitRunner.class)
public class MockitoSpyTest {

	@Test
	public void verifyMethodIsCalledWithoutCallingRealImpl() {
		TestObject1 spy = spy(new TestObject1());
		doNothing().when(spy).print();

		spy.doIt();

		verify(spy).doIt();
		verify(spy).print();
	}

	@Test
	public void verifyDecoratingAnObjectWithoutActuallyCallingConstructor() {
		TestObject2 spy = spy(new TestObject2());
		TestObject2 decorated = mock(TestObject2.class);

		doReturn(decorated).when(spy).wrapIt(spy);

		spy.wrap();

		verify(spy).wrapIt(spy);
		verify(decorated).print();
	}

	public static class TestObject1 {

		public void doIt() {
			print();
		}

		void print() {
			throw new RuntimeException("PRINT: OH NO!");
		}
	}

	public static class TestObject2 {

		public void wrap() {
			wrapIt(this).print();
		}

		public TestObject2 wrapIt(TestObject2 user) {
			return new DecoratedTestObject2(user);
		}

		void print() {
			throw new RuntimeException("PRINT: OH NO!");
		}

		public static class DecoratedTestObject2 extends TestObject2 {
			public DecoratedTestObject2(TestObject2 user) {
				throw new RuntimeException("DECORATOR CONSTRUCTOR: OH NO!");
			}
		}
	}
}