How to doNothing() on void method?

Question

I have a method that call a void function in it, and when I use doNothing(), it says that void method it's not allowed. How could I doNothing() in that specific line?

I'm using this line,

when(spyColorSelector.initializeColors(view, "red")).then(doNothing());

Answer 1

Use Stubber syntax :

doNothing().when(spyColorSelector).initializeColors(view, "red");

And spyColorSelector has to be a mock.

---

Edit 1: code example with spy.

This test works (no exception thrown by initializeColors) with JUnit 4.12 and Mockito 1.10.19:

public class ColorSelectorTest {

    @Test
    public void testGetColors() {
        // Given
        String color = "red";
        View view = mock(View.class);
        ColorSelector colorSelector = new ColorSelector();
        ColorSelector spyColorSelector = spy(colorSelector);
        doNothing().when(spyColorSelector).initializeColors(view, color);

        // When
        LinkedList<Integer> colors = spyColorSelector.getColors(color, view);

        // Then
        assertNotNull(colors);
    }
}

class ColorSelector {

    public LinkedList<Integer> getColors(String color, View view) {
        this.initializeColors(view, color);
        return new LinkedList<>();
    }

    void initializeColors(View view, String color) {
        throw new UnsupportedOperationException("Should not be called");
    }
}

---

Edit 2: new example without spy.

If you really want initializeColors not to be executed in the test, I think there is a design issue in the ColorSelector class. The initializeColors method should be in another class X, and there would be a dependency of class X in ColorSelector class which you could stub in your test (and then no need of spy). Basic example:

public class ColorSelectorTest {

    @Test
    public void testGetColors() {
        // Given
        String color = "red";
        View view = mock(View.class);
        ColorSelector colorSelector = new ColorSelector();
        ColorInitializer colorInitializerMock = mock(ColorInitializer.class);
        doNothing().when(colorInitializerMock).initializeColors(view, color);   // Optional because the default behavior of a mock is to do nothing
        colorSelector.colorInitializer = colorInitializerMock;

        // When
        LinkedList<Integer> colors = colorSelector.getColors(color, view);

        // Then
        assertNotNull(colors);
    }
}

class ColorSelector {

    ColorInitializer colorInitializer;

    public LinkedList<Integer> getColors(String color, View view) {
        colorInitializer.initializeColors(view, color);
        return new LinkedList<>();
    }
}

class ColorInitializer {

    public void initializeColors(View view, String color) {
        // Do something
    }
}