Configure Mockito to, by default, throw an exception when un-mocked behavior is invoked.

MockitoConfiguration

package org.mockito.configuration;

import org.mockito.Mockito;
import org.mockito.stubbing.Answer;

public class MockitoConfiguration extends DefaultMockitoConfiguration {
    @Override
    public Answer<Object> getDefaultAnswer() {
        return Mockito.RETURNS_SMART_NULLS;
    }
}