add delete timeout test

The timeout value is still not being persisted.

While it doesn't fix this issue, make sure to always return Private
during Plan.

builtin/providers/test/resource_timeout_test.go

@@ -27,6 +27,27 @@ resource "test_resource_timeout" "foo" {
 		},
 	})
 }
+
+func TestResourceTimeout_delete(t *testing.T) {
+	// If the delete timeout isn't saved until destroy, the cleanup here will
+	// fail because the default is only 20m.
+	resource.UnitTest(t, resource.TestCase{
+		Providers:    testAccProviders,
+		CheckDestroy: testAccCheckResourceDestroy,
+		Steps: []resource.TestStep{
+			resource.TestStep{
+				Config: strings.TrimSpace(`
+resource "test_resource_timeout" "foo" {
+	delete_delay = "25m"
+	timeouts {
+		delete = "30m"
+	}
+}
+				`),
+			},
+		},
+	})
+}
 func TestResourceTimeout_update(t *testing.T) {
 	resource.UnitTest(t, resource.TestCase{
 		Providers:    testAccProviders,

helper/plugin/grpc_provider.go

@@ -574,6 +574,7 @@ func (s *GRPCProviderServer) PlanResourceChange(_ context.Context, req *proto.Pl
 	// We don't usually plan destroys, but this can return early in any case.
 	if proposedNewStateVal.IsNull() {
 		resp.PlannedState = req.ProposedNewState
+		resp.PlannedPrivate = req.PriorPrivate
 		return resp, nil
 	}