feat: SQL server beta and templates refactoring (#32)

## Description

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At least please give us some description what you are trying to achieve and why your change is needed. -->

relates to #1234

## Checklist

- [ ] Issue was linked above
- [ ] Code format was applied: `make fmt`
- [ ] Examples were added / adjusted (see `examples/` directory)
- [x] Docs are up-to-date: `make generate-docs` (will be checked by CI)
- [ ] Unit tests got implemented or updated
- [ ] Acceptance tests got implemented or updated (see e.g. [here](f5f99d1709/stackit/internal/services/dns/dns_acc_test.go))
- [x] Unit tests are passing: `make test` (will be checked by CI)
- [x] No linter issues: `make lint` (will be checked by CI)

Reviewed-on: #32
Reviewed-by: Andre_Harms <andre.harms@stackit.cloud>
Co-authored-by: Marcel S. Henselin <marcel.henselin@stackit.cloud>
Co-committed-by: Marcel S. Henselin <marcel.henselin@stackit.cloud>

stackit/internal/services/sqlserverflexbeta/flavor/functions_test.go

@@ -0,0 +1,134 @@
+package sqlserverFlexBetaFlavor
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stackitcloud/stackit-sdk-go/core/utils"
+	"tf-provider.git.onstackit.cloud/stackit-dev-tools/terraform-provider-stackitprivatepreview/pkg_gen/sqlserverflexbeta"
+)
+
+type mockRequest struct {
+	executeFunc func() (*sqlserverflexbeta.GetFlavorsResponse, error)
+}
+
+func (m *mockRequest) Page(_ int64) sqlserverflexbeta.ApiGetFlavorsRequestRequest { return m }
+func (m *mockRequest) Size(_ int64) sqlserverflexbeta.ApiGetFlavorsRequestRequest { return m }
+func (m *mockRequest) Sort(_ sqlserverflexbeta.FlavorSort) sqlserverflexbeta.ApiGetFlavorsRequestRequest {
+	return m
+}
+func (m *mockRequest) Execute() (*sqlserverflexbeta.GetFlavorsResponse, error) {
+	return m.executeFunc()
+}
+
+type mockFlavorsClient struct {
+	executeRequest func() sqlserverflexbeta.ApiGetFlavorsRequestRequest
+}
+
+func (m *mockFlavorsClient) GetFlavorsRequest(_ context.Context, _, _ string) sqlserverflexbeta.ApiGetFlavorsRequestRequest {
+	return m.executeRequest()
+}
+
+var mockResp = func(page int64) (*sqlserverflexbeta.GetFlavorsResponse, error) {
+	if page == 1 {
+		return &sqlserverflexbeta.GetFlavorsResponse{
+			Flavors: &[]sqlserverflexbeta.ListFlavors{
+				{Id: utils.Ptr("flavor-1"), Description: utils.Ptr("first")},
+				{Id: utils.Ptr("flavor-2"), Description: utils.Ptr("second")},
+			},
+		}, nil
+	}
+	if page == 2 {
+		return &sqlserverflexbeta.GetFlavorsResponse{
+			Flavors: &[]sqlserverflexbeta.ListFlavors{
+				{Id: utils.Ptr("flavor-3"), Description: utils.Ptr("three")},
+			},
+		}, nil
+	}
+
+	return &sqlserverflexbeta.GetFlavorsResponse{
+		Flavors: &[]sqlserverflexbeta.ListFlavors{},
+	}, nil
+}
+
+func TestGetFlavorsByFilter(t *testing.T) {
+	tests := []struct {
+		description string
+		projectId   string
+		region      string
+		mockErr     error
+		filter      func(sqlserverflexbeta.ListFlavors) bool
+		wantCount   int
+		wantErr     bool
+	}{
+		{
+			description: "Success - Get all flavors (2 pages)",
+			projectId:   "pid", region: "reg",
+			filter:    func(_ sqlserverflexbeta.ListFlavors) bool { return true },
+			wantCount: 3,
+			wantErr:   false,
+		},
+		{
+			description: "Success - Filter flavors by description",
+			projectId:   "pid", region: "reg",
+			filter:    func(f sqlserverflexbeta.ListFlavors) bool { return *f.Description == "first" },
+			wantCount: 1,
+			wantErr:   false,
+		},
+		{
+			description: "Error - Missing parameters",
+			projectId:   "", region: "reg",
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(
+			tt.description, func(t *testing.T) {
+				var currentPage int64
+				client := &mockFlavorsClient{
+					executeRequest: func() sqlserverflexbeta.ApiGetFlavorsRequestRequest {
+						return &mockRequest{
+							executeFunc: func() (*sqlserverflexbeta.GetFlavorsResponse, error) {
+								currentPage++
+								return mockResp(currentPage)
+							},
+						}
+					},
+				}
+				actual, err := getFlavorsByFilter(context.Background(), client, tt.projectId, tt.region, tt.filter)
+
+				if (err != nil) != tt.wantErr {
+					t.Errorf("getFlavorsByFilter() error = %v, wantErr %v", err, tt.wantErr)
+					return
+				}
+
+				if !tt.wantErr && len(actual) != tt.wantCount {
+					t.Errorf("getFlavorsByFilter() got %d flavors, want %d", len(actual), tt.wantCount)
+				}
+			},
+		)
+	}
+}
+
+func TestGetAllFlavors(t *testing.T) {
+	var currentPage int64
+	client := &mockFlavorsClient{
+		executeRequest: func() sqlserverflexbeta.ApiGetFlavorsRequestRequest {
+			return &mockRequest{
+				executeFunc: func() (*sqlserverflexbeta.GetFlavorsResponse, error) {
+					currentPage++
+					return mockResp(currentPage)
+				},
+			}
+		},
+	}
+
+	res, err := getAllFlavors(context.Background(), client, "pid", "reg")
+	if err != nil {
+		t.Errorf("getAllFlavors() unexpected error: %v", err)
+	}
+	if len(res) != 3 {
+		t.Errorf("getAllFlavors() expected 3 flavor, got %d", len(res))
+	}
+}