Advertise Write in tests and cover the write-not-advertised path

Now that the Write() advertisement gate is present in the Hvac feature
helper, the test fixture must advertise the Write operation for existing
write tests to pass, and a dedicated test verifies WriteOperationMode
returns ErrNotSupported when the remote advertises the system-function
list as read-only.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: andig

usecases/ca/cdsf/public_test.go

@@ -1,6 +1,7 @@
 package cdsf
 
 import (
+	"github.com/enbility/eebus-go/api"
 	ucapi "github.com/enbility/eebus-go/usecases/api"
 	"github.com/enbility/spine-go/model"
 	"github.com/enbility/spine-go/util"
@@ -156,6 +157,23 @@ func (s *CaCDSFSuite) Test_WriteOperationMode_AmbiguousSystemFunction() {
 	assert.NotNil(s.T(), err)
 }
 
+func (s *CaCDSFSuite) Test_WriteOperationMode_WriteNotAdvertised() {
+	s.addHvacData(util.Ptr(true))
+
+	// re-advertise the system-function list as read-only
+	rFeature := s.remoteDevice.FeatureByEntityTypeAndRole(s.dhwCircuitEntity, model.FeatureTypeTypeHvac, model.RoleTypeServer)
+	rFeature.SetOperations([]model.FunctionPropertyType{
+		{
+			Function:           util.Ptr(model.FunctionTypeHvacSystemFunctionListData),
+			PossibleOperations: &model.PossibleOperationsType{Read: &model.PossibleOperationsReadType{}},
+		},
+	})
+
+	// the write must be rejected when the remote does not advertise Write()
+	_, err := s.sut.WriteOperationMode(s.dhwCircuitEntity, ucapi.HvacOperationModeTypeOn, nil)
+	assert.ErrorIs(s.T(), err, api.ErrNotSupported)
+}
+
 // helpers
 
 func (s *CaCDSFSuite) addOverrunData(isChangeable bool) {

usecases/ca/cdsf/testhelper_test.go

@@ -116,7 +116,8 @@ func setupDevices(
 			supportedFct := model.FunctionPropertyType{
 				Function: util.Ptr(fct),
 				PossibleOperations: &model.PossibleOperationsType{
-					Read: &model.PossibleOperationsReadType{},
+					Read:  &model.PossibleOperationsReadType{},
+					Write: &model.PossibleOperationsWriteType{},
 				},
 			}
 			supportedFcts = append(supportedFcts, supportedFct)