@Override
        protected DuoSecurityAuthenticationResult authenticateInternal(final Credential credential) {
            return null;
        }
This is {@link DuoSecurityAuthenticationServiceTests}.

@author Misagh Moayyed
@since 7.0.0
support/cas-server-support-duo-core/src/test/java/org/apereo/cas/adaptors/duo/authn/DuoSecurityAuthenticationServiceTests.java