Fix harmful nesting spy on RootWindowContainer

import androidx.test.filters.SmallTest;

import org.junit.AfterClass;

import org.junit.Before;

import org.junit.BeforeClass;

import org.junit.Test;

/**

@Presubmit

public class AppTransitionTests extends WindowTestsBase {

    private static RootWindowContainer sOriginalRootWindowContainer;

    private DisplayContent mDc;

    @BeforeClass

    public static void setUpRootWindowContainerMock() {

        final WindowManagerService wm = WmServiceUtils.getWindowManagerService();

        // For unit test, we don't need to test performSurfacePlacement to prevent some abnormal

        // interaction with surfaceflinger native side.

        sOriginalRootWindowContainer = wm.mRoot;

        // Creating spied mock of RootWindowContainer shouldn't be done in @Before, since it will

        // create unnecessary nested spied objects chain, because WindowManagerService object under

        // test is a single instance shared among all tests that extend WindowTestsBase class.

        // Instead it should be done once before running all tests in this test class.

        wm.mRoot = spy(wm.mRoot);

        doNothing().when(wm.mRoot).performSurfacePlacement(anyBoolean());

    }

    @AfterClass

    public static void tearDownRootWindowContainerMock() {

        final WindowManagerService wm = WmServiceUtils.getWindowManagerService();

        wm.mRoot = sOriginalRootWindowContainer;

        sOriginalRootWindowContainer = null;

    }

    @Before

    public void setUp() throws Exception {

        mDc = mWm.getDefaultDisplayContentLocked();

        // For unit test,  we don't need to test performSurfacePlacement to prevent some

        // abnormal interaction with surfaceflinger native side.

        mWm.mRoot = spy(mWm.mRoot);

        doNothing().when(mWm.mRoot).performSurfacePlacement(anyBoolean());

    }

    @Test