@Test
    void verifyBadCredentialsOperation() throws Throwable {
        val registeredService = addRegisteredService();
        val body = (OAuth20IntrospectionAccessTokenFailureResponse) internalVerifyOperation("---", registeredService);
        assertNotNull(body.getError());
    }
This is {@link OAuth20IntrospectionEndpointControllerTests}.

@author Misagh Moayyed
@since 6.1.0
support/cas-server-support-oauth/src/test/java/org/apereo/cas/support/oauth/web/endpoints/OAuth20IntrospectionEndpointControllerTests.java