add basic unit tests for templating

internal/sync/templating/templating_test.go

@@ -0,0 +1,86 @@
+/*
+Copyright 2025 The KCP Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package templating
+
+import (
+	"testing"
+
+	"github.com/kcp-dev/logicalcluster/v3"
+
+	"github.com/kcp-dev/api-syncagent/test/crds"
+	"github.com/kcp-dev/api-syncagent/test/utils"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+)
+
+func TestRender(t *testing.T) {
+	clusterName := logicalcluster.Name("12386rtr4u")
+	clusterPath := logicalcluster.NewPath("root:yadda:yadda")
+
+	crontab := &crds.Crontab{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      "my-crontab",
+			Namespace: "default",
+		},
+		Spec: crds.CrontabSpec{
+			Image: "ubuntu:latest",
+		},
+	}
+
+	object := utils.ToUnstructured(t, crontab)
+	object.SetAPIVersion("kcp.example.com/v1")
+	object.SetKind("CronTab")
+
+	testcases := []struct {
+		name     string
+		template string
+		data     any
+		expected string
+	}{
+		{
+			name:     "simple object access",
+			data:     newLocalObjectNamingContext(object, clusterName, clusterPath),
+			template: `{{ .Object.spec.image }}`,
+			expected: crontab.Spec.Image,
+		},
+		{
+			name:     "default empty fields",
+			data:     newLocalObjectNamingContext(object, clusterName, clusterPath),
+			template: `{{ .Object.spec.spec | default "test" }}`,
+			expected: "test",
+		},
+		{
+			name:     "default non-existing field",
+			data:     newLocalObjectNamingContext(object, clusterName, clusterPath),
+			template: `{{ .Object.does.not.exist | default "test" }}`,
+			expected: "test",
+		},
+	}
+
+	for _, testcase := range testcases {
+		t.Run(testcase.name, func(t *testing.T) {
+			rendered, err := Render(testcase.template, testcase.data)
+			if err != nil {
+				t.Fatalf("Unexpected error: %v.", err)
+			}
+
+			if rendered != testcase.expected {
+				t.Errorf("Expected %q, but got %q.", testcase.expected, rendered)
+			}
+		})
+	}
+}