def test_register_valid_class(self):
        """Test backend registration for a custom valid backend."""
        backend_name = register_backend(ValidBackend)

        # Check that it has been added to the list of backends.
        self.assertIn(backend_name, _REGISTERED_BACKENDS.keys())
        self.assertEqual(_REGISTERED_BACKENDS[backend_name].cls, ValidBackend)

        # Second registration should fail as it is already registered.
        with self.assertRaises(QISKitError):
            register_backend(ValidBackend)
    def test_register_valid_class(self):
        """Test backend registration for a custom valid backend."""
        backend_name = register_backend(ValidBackend)

        # Check that it has been added to the list of backends.
        self.assertIn(backend_name, _REGISTERED_BACKENDS.keys())
        self.assertEqual(_REGISTERED_BACKENDS[backend_name].cls, ValidBackend)

        # Second registration should fail as it is already registered.
        with self.assertRaises(QISKitError):
            register_backend(ValidBackend)