"Argument should be a mock, but is" error when combine @InjectMocks with @Spy

In mockito <=2.0.12 there was possible to use @InjectMocks on spy object, but seems like this was changed since 2.0.13-beta version:

Argument should be a mock, but is: class mockito.bug.snippet.ArgumentShouldBeAMockButIsTest$B

Test case:

package mockito.bug.snippet;

import org.junit.Before;
import org.junit.Test;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.MockitoAnnotations;
import org.mockito.Spy;

public class ArgumentShouldBeAMockButIsTest {

    // Inject here
    static class A {
        private B b;
    }

    // Inject here also
    static class B {
        private C c;
    }

    // Some dependency
    static class C {
    }

    @InjectMocks
    private final A a = new A();

    @Spy
    @InjectMocks
    private final B b = new B();

    @Mock
    private C c;

    @Before
    public void setUp() throws Exception {
        MockitoAnnotations.initMocks(this);
    }

    @Test
    // Worked in 2.0.12-beta
    public void testArgumentShouldBeAMockButIsNonMock() {
        b.toString();
    }
}

[jebeaudet]

So what is Mockito official stance on using @InjectMocks with @Spy? The javadoc still references it as being supported (https://github.com/mockito/mockito/blob/release/3.x/src/main/java/org/mockito/InjectMocks.java#L140) but it doesn’t work by using both annotations on a field. I don’t mind doing the workaround mentioned above with Mockito.spy(new B()) instead of the annotations while this bug is being fixed but I’d like a definitive answer since that bug has been opened for a while now!

Thanks!

[kcharlampowicz]

I’ve just noticed that there is still this misbehavior (undocumented feature) when you provide spy object by hand. If you run test provided by @vbuell with object created by Mockito#spy method then test passes (of course it’s not important if there is @Spy annotation on that field).

I’ve reproduced this issue on latest Mockito version: 2.7.14

import org.junit.Before;
import org.junit.Test;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.Mockito;
import org.mockito.MockitoAnnotations;
import org.mockito.Spy;

public class ArgumentShouldBeAMockButIsTest {

	// Inject here
	static class A {
		private B b;
	}

	// Inject here also
	static class B {
		private C c;
	}

	// Some dependency
	static class C {
	}

	@InjectMocks
	private final A a = new A();

	@Spy
	@InjectMocks
	private final B b = Mockito.spy(new B());

	@Mock
	private C c;

	@Before
	public void setUp() throws Exception {
		MockitoAnnotations.initMocks(this);
	}

	@Test
	//Test passed
	public void testArgumentShouldBeAMockButIsNonMock() {
		b.toString();
	}
}