[CDTOOL-1202] Correct 'TestAccResourceFastlyTLSSubscription_Config' Failure (#1135)

* apply check to update

* changelog update

Author: rcaril

CHANGELOG.md

@@ -14,6 +14,7 @@
 - fix(backend): preserve optional bool fields (`use_ssl`, `ssl_check_cert`, `prefer_ipv6`, `auto_loadbalance`) during updates and add acceptance test coverage ([#1133](https://github.com/fastly/terraform-provider-fastly/pull/1133))
 - fix(domains_v1/service_link): corrected a behavior where new service links created were not referring to 'domain_id' values correctly ([#1132](https://github.com/fastly/terraform-provider-fastly/pull/1132))
 - fix(logging/compute): corrected drift behavior for some compute logging endpoints where the value of 'period' was not being retained correctly ([#1134](https://github.com/fastly/terraform-provider-fastly/pull/1134))
+- fix(tls/subscriptions): corrects 'common_name' validation for update operations ([#1135](https://github.com/fastly/terraform-provider-fastly/pull/1135))
 
 ### DEPENDENCIES:
 

fastly/resource_fastly_tls_subscription.go

@@ -370,14 +370,22 @@ func resourceFastlyTLSSubscriptionUpdate(ctx context.Context, d *schema.Resource
 		// field on the input struct if there was a change because we otherwise
 		// can't guarantee the order.
 		var domains []*gofastly.TLSDomain
+		var domainStrings []string
 		for _, domain := range d.Get("domains").(*schema.Set).List() {
 			domains = append(domains, &gofastly.TLSDomain{ID: domain.(string)})
+			domainStrings = append(domainStrings, domain.(string))
+		}
+
+		// Validate that common_name is in domains
+		commonNameStr := d.Get("common_name").(string)
+		if commonNameStr != "" && !contains(domainStrings, commonNameStr) {
+			return diag.Errorf("domain specified as common_name (%s) must also be in domains (%v)", commonNameStr, domainStrings)
 		}
 
 		updates := &gofastly.UpdateTLSSubscriptionInput{
 			ID:         d.Id(),
 			Force:      d.Get("force_update").(bool),
-			CommonName: &gofastly.TLSDomain{ID: d.Get("common_name").(string)},
+			CommonName: &gofastly.TLSDomain{ID: commonNameStr},
 			Domains:    domains,
 
 			// IMPORTANT: We should always pass the configuration_id to the API.

fastly/resource_fastly_tls_subscription_test.go

@@ -67,7 +67,7 @@ func TestAccResourceFastlyTLSSubscription_Config(t *testing.T) {
 			},
 			{
 				Config:      testAccResourceFastlyTLSSubscriptionConfigInvalidCommonName(),
-				ExpectError: regexp.MustCompile(`Please add \S+ to an active service to begin TLS enablement`),
+				ExpectError: regexp.MustCompile(`domain specified as common_name .* must also be in domains`),
 			},
 			{
 				Config:      testAccResourceFastlyTLSSubscriptionConfig(name, domain1, domain2Bad, commonName2),