fix: Add validation for transport types in ClientFactory

src/a2a/client/client_factory.py

@@ -91,7 +91,7 @@ def _register_defaults(
             if GrpcTransport is None:
                 raise ImportError(
                     'To use GrpcClient, its dependencies must be installed. '
-                    'You can install them with \'pip install "a2a-sdk[grpc]"\''
+                    'You can install them with \'pip install "a2a-sdk[grpc]"\'',
                 )
             self.register(
                 TransportProtocol.grpc,
@@ -124,6 +124,14 @@ def create(
           If there is no valid matching of the client configuration with the
           server configuration, a `ValueError` is raised.
         """
+        valid_transports = {member.value for member in TransportProtocol}
+        for transport in self._config.supported_transports:
+            if transport not in valid_transports:
+                raise ValueError(
+                    f"Unsupported transport type in ClientConfig: '{transport}'. "
+                    f'Valid types are: {", ".join(sorted(valid_transports))}',
+                )
+
         server_preferred = card.preferred_transport or TransportProtocol.jsonrpc
         server_set = {server_preferred: card.url}
         if card.additional_interfaces:

tests/client/test_client_factory.py

@@ -103,3 +103,19 @@ def test_client_factory_no_compatible_transport(base_agent_card: AgentCard):
     factory = ClientFactory(config)
     with pytest.raises(ValueError, match='no compatible transports found'):
         factory.create(base_agent_card)
+
+
+def test_client_factory_invalid_transport_in_config(base_agent_card: AgentCard):
+    """Verify that the factory raises an error for an unknown transport type."""
+    config = ClientConfig(
+        httpx_client=httpx.AsyncClient(),
+        supported_transports=[
+            TransportProtocol.jsonrpc,
+            'invalid-transport-protocol',
+        ],
+    )
+    factory = ClientFactory(config)
+    with pytest.raises(
+        ValueError, match='Unsupported transport type in ClientConfig'
+    ):
+        factory.create(base_agent_card)