Feature: CDN custom domain resource and data source (#801)

* Feature: CDN custom domain resource and data source

* stabilize acceptance tests

* add guide

* review changes

---------

Co-authored-by: Malte Ehrlen <malte.ehrlen@freiheit.com>

stackit/internal/services/cdn/customdomain/resource_test.go

@@ -0,0 +1,90 @@
+package cdn
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/hashicorp/terraform-plugin-framework/attr"
+	"github.com/hashicorp/terraform-plugin-framework/types"
+	"github.com/stackitcloud/stackit-sdk-go/services/cdn"
+)
+
+func TestMapFields(t *testing.T) {
+	emtpyErrorsList := types.ListValueMust(types.StringType, []attr.Value{})
+	expectedModel := func(mods ...func(*CustomDomainModel)) *CustomDomainModel {
+		model := &CustomDomainModel{
+			ID:             types.StringValue("test-project-id,test-distribution-id,https://testdomain.com"),
+			DistributionId: types.StringValue("test-distribution-id"),
+			ProjectId:      types.StringValue("test-project-id"),
+			Status:         types.StringValue("ACTIVE"),
+			Errors:         emtpyErrorsList,
+		}
+		for _, mod := range mods {
+			mod(model)
+		}
+		return model
+	}
+	customDomainFixture := func(mods ...func(*cdn.CustomDomain)) *cdn.CustomDomain {
+		distribution := &cdn.CustomDomain{
+			Errors: &[]cdn.StatusError{},
+			Name:   cdn.PtrString("https://testdomain.com"),
+			Status: cdn.DOMAINSTATUS_ACTIVE.Ptr(),
+		}
+		for _, mod := range mods {
+			mod(distribution)
+		}
+		return distribution
+	}
+	tests := map[string]struct {
+		Input    *cdn.CustomDomain
+		Expected *CustomDomainModel
+		IsValid  bool
+	}{
+		"happy_path": {
+			Expected: expectedModel(),
+			Input:    customDomainFixture(),
+			IsValid:  true,
+		},
+		"happy_path_status_error": {
+			Expected: expectedModel(func(m *CustomDomainModel) {
+				m.Status = types.StringValue("ERROR")
+			}),
+			Input: customDomainFixture(func(d *cdn.CustomDomain) {
+				d.Status = cdn.DOMAINSTATUS_ERROR.Ptr()
+			}),
+			IsValid: true,
+		},
+		"sad_path_custom_domain_nil": {
+			Expected: expectedModel(),
+			Input:    nil,
+			IsValid:  false,
+		},
+		"sad_path_name_missing": {
+			Expected: expectedModel(),
+			Input: customDomainFixture(func(d *cdn.CustomDomain) {
+				d.Name = nil
+			}),
+			IsValid: false,
+		},
+	}
+	for tn, tc := range tests {
+		t.Run(tn, func(t *testing.T) {
+			model := &CustomDomainModel{}
+			model.DistributionId = tc.Expected.DistributionId
+			model.ProjectId = tc.Expected.ProjectId
+			err := mapCustomDomainFields(tc.Input, model)
+			if err != nil && tc.IsValid {
+				t.Fatalf("Error mapping fields: %v", err)
+			}
+			if err == nil && !tc.IsValid {
+				t.Fatalf("Should have failed")
+			}
+			if tc.IsValid {
+				diff := cmp.Diff(model, tc.Expected)
+				if diff != "" {
+					t.Fatalf("Create Payload not as expected: %s", diff)
+				}
+			}
+		})
+	}
+}