Use Powermockito to check if a private method is called or not

I would like to check if a private method of my class to test is executed or not using powermockito.

Suppose that I have this class to test:

public class ClassToTest {
    public boolean methodToTest() {
        //doSomething (maybe call privateMethod or maybeNot)
        return true;
    }

    //I want to know if this is called or not during the test of "methodToTest".
    private void privateMethod() {
        //do something
    }
}

When I test "methodToTest" I want to check if it returns the correct result but also if it executes the private method "privateMethod" or not. Searching on other discussion I wrote this test that makes use of powermockito but it doesnt works.

public class TestClass {

    @Test
    testMethodToTest(){
        ClassToTest instance = new ClassToTest();
        boolean result = instance.methodToTest();
        assertTrue(result, "The public method must return true");

        //Checks if the public method "methodToTest" called "privateMethod" during its execution.
        PowerMockito.verifyPrivate(instance, times(1)).invoke("privateMethod");
    }
}

When I use the debugger it seems that the last line (PowerMockito.verifyPrivate...) doesn't check if the private method has been executed once during the test but instead it seems that it executes the private method itself. Furthermore the test passes but using the debugger I'm sure that the private method is not executed during the call of "instance.methodToTest()". What is wrong?