test: add acceptance test for repeated registrant contact_id changes

Add TestAccRegisteredDomainResource_RepeatedRegistrantChange to cover
the scenario where contact_id is updated multiple times. Previously,
the second update would fail with 'unexpected unknown property value
for registrantChange'.

Also fix misleading comment in update.go about createRegistrantChange
being called unconditionally after convergence.

Signed-off-by: Maksim Ryzhukhin <mryzhukhin@rightandabove.com>

Author: Maksim Ryzhukhin

internal/framework/resources/registered_domain/resource_test.go

@@ -142,6 +142,51 @@ func TestAccRegisteredDomainResource_RegistrantChange_WithExtendedAttrs(t *testi
 	})
 }
 
+func TestAccRegisteredDomainResource_RepeatedRegistrantChange(t *testing.T) {
+	domainName := os.Getenv("DNSIMPLE_REGISTRANT_CHANGE_DOMAIN")
+	contactID := os.Getenv("DNSIMPLE_REGISTRANT_CHANGE_CONTACT_ID")
+	contactID2 := os.Getenv("DNSIMPLE_REGISTRANT_CHANGE_CONTACT_ID_2")
+	resourceName := "dnsimple_registered_domain.test"
+
+	resource.Test(t, resource.TestCase{
+		PreCheck:                 func() { testAccPreCheckRepeatedRegistrantChange(t) },
+		ProtoV6ProviderFactories: test_utils.TestAccProtoV6ProviderFactories(),
+		CheckDestroy:             testAccCheckRegisteredDomainRegistrantChangeDestroy,
+		Steps: []resource.TestStep{
+			{
+				// Import the existing domain
+				ResourceName:       resourceName,
+				Config:             testAccRegisteredDomainResourceConfig(domainName, "1234"),
+				ImportStateId:      domainName,
+				ImportState:        true,
+				ImportStateVerify:  false,
+				ImportStatePersist: true,
+			},
+			{
+				// First contact_id change
+				Config: testAccRegisteredDomainResourceConfig(domainName, contactID),
+				Check: resource.ComposeAggregateTestCheckFunc(
+					resource.TestCheckResourceAttr(resourceName, "name", domainName),
+					resource.TestCheckResourceAttrSet(resourceName, "registrant_change.id"),
+					resource.TestCheckResourceAttr(resourceName, "registrant_change.contact_id", contactID),
+				),
+				ExpectNonEmptyPlan: true,
+			},
+			{
+				// Second contact_id change - previously failed with:
+				// "unexpected unknown property value for registrantChange"
+				Config: testAccRegisteredDomainResourceConfig(domainName, contactID2),
+				Check: resource.ComposeAggregateTestCheckFunc(
+					resource.TestCheckResourceAttr(resourceName, "name", domainName),
+					resource.TestCheckResourceAttrSet(resourceName, "registrant_change.id"),
+					resource.TestCheckResourceAttr(resourceName, "registrant_change.contact_id", contactID2),
+				),
+				ExpectNonEmptyPlan: true,
+			},
+		},
+	})
+}
+
 func TestAccRegisteredDomainResource_WithOptions(t *testing.T) {
 	domainName := utils.RandomName("com", "options")
 	contactID := os.Getenv("DNSIMPLE_CONTACT_ID")
@@ -217,6 +262,13 @@ func testAccPreCheckRegistrantChange(t *testing.T) {
 	}
 }
 
+func testAccPreCheckRepeatedRegistrantChange(t *testing.T) {
+	testAccPreCheckRegistrantChange(t)
+	if os.Getenv("DNSIMPLE_REGISTRANT_CHANGE_CONTACT_ID_2") == "" {
+		t.Fatal("DNSIMPLE_REGISTRANT_CHANGE_CONTACT_ID_2 must be set for acceptance tests")
+	}
+}
+
 func testAccRegisteredDomainImportStateIDFunc(resourceName string) resource.ImportStateIdFunc {
 	return func(s *terraform.State) (string, error) {
 		rs, ok := s.RootModule().Resources[resourceName]

internal/framework/resources/registered_domain/update.go

@@ -156,7 +156,8 @@ func (r *RegisteredDomainResource) Update(ctx context.Context, req resource.Upda
 				return
 			}
 		}
-		// Create a new registrant change (either no previous change exists or previous one is already completed)
+		// Pending registrant change has been converged or no pending change exists.
+		// Always create a new registrant change when contact_id differs.
 		createRegistrantChange(ctx, planData, r, resp)
 	} else if !registrantChange.Id.IsNull() && registrantChange.State.ValueString() != consts.RegistrantChangeStateCompleted {
 		registrantChangeResponse, err = r.config.Client.Registrar.GetRegistrantChange(ctx, r.config.AccountID, int(registrantChange.Id.ValueInt64()))