test: cover a failed server delete during machine deletion

The delete path removes the finalizer only after the cloud reports the
server as deleted or as already gone. The other exit had no spec: a
deletion that answers with any other error must keep the object.

The new spec injects a transient error into the server delete, then
asserts that the reconcile returns that error, that the server is still
there, and that the finalizer still holds the object, so the next
attempt can find the instance ID.

Author: corioliskraft

controller/stackitmachine_controller_test.go

@@ -461,6 +461,33 @@ var _ = Describe("StackitMachine Controller", func() {
 		}).Should(BeTrue())
 	})
 
+	It("keeps the finalizer when the server deletion fails", func() {
+		// The delete path removes the finalizer only after the cloud reports the
+		// server as deleted or as already gone. Any other delete error leaves the
+		// server running, so the object must stay and the reconcile must retry.
+		// Without the object, nothing holds the instance ID and the VM keeps
+		// running unnoticed.
+		updateMachineBootstrapSecret(ctx, machineName, bootstrapName)
+		createBootstrapSecret(ctx, bootstrapName)
+
+		_, err := reconciler.Reconcile(ctx, request)
+		Expect(err).NotTo(HaveOccurred())
+		Expect(fakeCloud.ServerCount()).To(Equal(1))
+
+		got := &infrav1.StackitMachine{}
+		Expect(k8sClient.Get(ctx, stackitKey, got)).To(Succeed())
+		fakeCloud.FailNextDeleteServer = fmt.Errorf("delete server: %w", cloud.ErrTransient)
+
+		Expect(k8sClient.Delete(ctx, got)).To(Succeed())
+		_, err = reconciler.Reconcile(ctx, request)
+
+		Expect(err).To(MatchError(cloud.ErrTransient))
+		Expect(fakeCloud.ServerCount()).To(Equal(1))
+		stillThere := &infrav1.StackitMachine{}
+		Expect(k8sClient.Get(ctx, stackitKey, stillThere)).To(Succeed())
+		Expect(stillThere.Finalizers).To(ContainElement(infrav1.MachineFinalizer))
+	})
+
 	It("maps owning Machine events to StackitMachine reconcile requests", func() {
 		machine := &clusterv1.Machine{}
 		Expect(k8sClient.Get(ctx, types.NamespacedName{Name: machineName, Namespace: namespace}, machine)).To(Succeed())