}

    /**
     * Check if a registration exists
     *
     * @param registrationId the registration ID
     * @return true if registration exists
     */
    public boolean hasRegistration(String registrationId) {
        return registrations.containsKey(registrationId);
    }

    /**
     * Simulate sending a witness notification
     *
     * @param eventType the event type

        assertTrue(mockService.hasRegistration(reg1));
        assertTrue(mockService.hasRegistration(reg2));
        assertTrue(mockService.hasRegistration(reg3));

        // Unregister one
        assertTrue(mockService.unregisterWitness(reg2));
        assertEquals(2, mockService.getRegistrationCount());
        assertFalse(mockService.hasRegistration(reg2));

        // Clean up remaining