tests: add testcase for immutable storagezone fields

Add a testcase that ensures changing an immutable storagezone field fails

internal/provider/resource_storagezone_test.go

@@ -2,6 +2,7 @@ package provider
 
 import (
 	"context"
+	"regexp"
 
 	"errors"
 	"fmt"
@@ -172,6 +173,94 @@ resource "bunny_storagezone" "%s" {
 	})
 }
 
+func TestChangingImmutableFieldsFails(t *testing.T) {
+	const resourceName = "mytest1"
+	const fullResourceName = "bunny_storagezone." + resourceName
+	storageZoneName := randStorageZoneName()
+
+	attrs := bunny.StorageZone{
+		Name:               ptr.ToString(storageZoneName),
+		Region:             ptr.ToString("NY"),
+		ReplicationRegions: []string{"DE"},
+	}
+
+	resource.Test(t, resource.TestCase{
+		Providers: testProviders,
+		Steps: []resource.TestStep{
+			// create storagezone
+			{
+				Config: fmt.Sprintf(`
+resource "bunny_storagezone" "mytest1" {
+	name = "%s"
+	region = "%s"
+	replication_regions = %s
+}
+`,
+					storageZoneName,
+					*attrs.Region,
+					tfStrList(attrs.ReplicationRegions),
+				),
+				Check: checkSzState(t, fullResourceName, &attrs),
+			},
+			// change region
+			{
+				Config: fmt.Sprintf(`
+resource "bunny_storagezone" "mytest1" {
+	name = "%s"
+	region = "LA"
+	replication_regions = ["DE"]
+}
+`,
+					storageZoneName,
+				),
+				ExpectError: regexp.MustCompile(".*'region' is immutable.*"),
+			},
+			// change name
+			{
+				Config: fmt.Sprintf(`
+resource "bunny_storagezone" "mytest1" {
+	name = "%s"
+	region = "LA"
+	replication_regions = ["DE"]
+}
+`,
+					storageZoneName+resource.UniqueId(),
+				),
+				Check:       checkSzState(t, fullResourceName, &attrs),
+				ExpectError: regexp.MustCompile(".*'name' is immutable.*"),
+			},
+			// replace a replication_region
+			{
+				Config: fmt.Sprintf(`
+resource "bunny_storagezone" "mytest1" {
+	name = "%s"
+	region = "NY"
+	replication_regions = ["LA"]
+}
+`,
+					storageZoneName,
+				),
+				Check:       checkSzState(t, fullResourceName, &attrs),
+				ExpectError: regexp.MustCompile(".*'replication_regions' can be added but not removed.*"),
+			},
+			// remove replication_region
+			{
+				Config: fmt.Sprintf(`
+resource "bunny_storagezone" "mytest1" {
+	name = "%s"
+	region = "NY"
+}
+`,
+					storageZoneName,
+				),
+				Check:       checkSzState(t, fullResourceName, &attrs),
+				ExpectError: regexp.MustCompile(".*'replication_regions' can be added but not removed.*"),
+			},
+		},
+		CheckDestroy: checkStorageZoneNotExists(fullResourceName),
+	})
+}
+
 func checkSzState(t *testing.T, resourceName string, wanted *bunny.StorageZone) resource.TestCheckFunc {
 	return func(s *terraform.State) error {
 		clt := newAPIClient()