LT ID immutable test case

Author: AmitSahastra

exp/webhooks/awsmanagedmachinepool_webhook_test.go

@@ -797,6 +797,49 @@ func TestAWSManagedMachinePoolValidateUpdate(t *testing.T) {
 			},
 			wantErr: true,
 		},
+		{
+			name: "setting BYO launch template ID on CAPA-managed LT is rejected",
+			old: &expinfrav1.AWSManagedMachinePool{
+				Spec: expinfrav1.AWSManagedMachinePoolSpec{
+					EKSNodegroupName: "eks-node-group-1",
+					AWSLaunchTemplate: &expinfrav1.AWSLaunchTemplate{
+						Name: "my-lt",
+					},
+				},
+			},
+			new: &expinfrav1.AWSManagedMachinePool{
+				Spec: expinfrav1.AWSManagedMachinePoolSpec{
+					EKSNodegroupName: "eks-node-group-1",
+					AWSLaunchTemplate: &expinfrav1.AWSLaunchTemplate{
+						Name:          "my-lt",
+						ID:            aws.String("lt-12345"),
+						VersionNumber: aws.Int64(1),
+					},
+				},
+			},
+			wantErr: true,
+		},
+		{
+			name: "removing BYO launch template ID is rejected",
+			old: &expinfrav1.AWSManagedMachinePool{
+				Spec: expinfrav1.AWSManagedMachinePoolSpec{
+					EKSNodegroupName: "eks-node-group-1",
+					AWSLaunchTemplate: &expinfrav1.AWSLaunchTemplate{
+						ID:            aws.String("lt-12345"),
+						VersionNumber: aws.Int64(1),
+					},
+				},
+			},
+			new: &expinfrav1.AWSManagedMachinePool{
+				Spec: expinfrav1.AWSManagedMachinePoolSpec{
+					EKSNodegroupName: "eks-node-group-1",
+					AWSLaunchTemplate: &expinfrav1.AWSLaunchTemplate{
+						Name: "my-lt",
+					},
+				},
+			},
+			wantErr: true,
+		},
 		{
 			name: "changing BYO launch template version is accepted",
 			old: &expinfrav1.AWSManagedMachinePool{