pkg: test ResourceBinding mutating webhook

In this commit, we introduce unit tests for the `MutatingAdmission`
webhook that mutates the `ResourceBinding` resource. These tests ensure
correct behavior for various mutation scenarios and improve coverage:

- Testing the handling of decode errors and ensuring that admission
is denied when decoding fails.
- Full coverage testing of policy mutation, including setting default
UUID labels for the `ResourceBinding`.
- Verifying that only the expected patch for the UUID label is applied,
ensuring no other unnecessary mutations.

Signed-off-by: Mohamed Awnallah <mohamedmohey2352@gmail.com>

pkg/webhook/resourcebinding/mutating_test.go

@@ -0,0 +1,183 @@
+/*
+Copyright 2024 The Karmada 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 resourcebinding
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"net/http"
+	"reflect"
+	"testing"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/runtime"
+	"sigs.k8s.io/controller-runtime/pkg/webhook/admission"
+
+	workv1alpha2 "github.com/karmada-io/karmada/pkg/apis/work/v1alpha2"
+)
+
+type fakeMutationDecoder struct {
+	err error
+	obj runtime.Object
+}
+
+// Decode mocks the Decode method of admission.Decoder.
+func (f *fakeMutationDecoder) Decode(_ admission.Request, obj runtime.Object) error {
+	if f.err != nil {
+		return f.err
+	}
+	if f.obj != nil {
+		reflect.ValueOf(obj).Elem().Set(reflect.ValueOf(f.obj).Elem())
+	}
+	return nil
+}
+
+// DecodeRaw mocks the DecodeRaw method of admission.Decoder.
+func (f *fakeMutationDecoder) DecodeRaw(_ runtime.RawExtension, obj runtime.Object) error {
+	if f.err != nil {
+		return f.err
+	}
+	if f.obj != nil {
+		reflect.ValueOf(obj).Elem().Set(reflect.ValueOf(f.obj).Elem())
+	}
+	return nil
+}
+
+func TestMutatingAdmission_Handle(t *testing.T) {
+	tests := []struct {
+		name    string
+		decoder admission.Decoder
+		req     admission.Request
+		want    admission.Response
+	}{
+		{
+			name: "Handle_DecodeError_DeniesAdmission",
+			decoder: &fakeMutationDecoder{
+				err: errors.New("decode error"),
+			},
+			req:  admission.Request{},
+			want: admission.Errored(http.StatusBadRequest, errors.New("decode error")),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			m := MutatingAdmission{
+				Decoder: tt.decoder,
+			}
+			got := m.Handle(context.Background(), tt.req)
+			if !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("Handle() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestMutatingAdmission_Handle_FullCoverage(t *testing.T) {
+	// Define the rb name and namespace to be used in the test.
+	name := "test-resource-binding"
+	namespace := "test-namespace"
+	podName := "test-pod"
+
+	// Mock an admission request.
+	req := admission.Request{}
+
+	// Create the initial rb object with default values for testing.
+	rb := &workv1alpha2.ResourceBinding{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      name,
+			Namespace: namespace,
+		},
+		Spec: workv1alpha2.ResourceBindingSpec{
+			Resource: workv1alpha2.ObjectReference{
+				APIVersion: "v1",
+				Kind:       "Pod",
+				Namespace:  namespace,
+				Name:       podName,
+			},
+			Clusters: []workv1alpha2.TargetCluster{
+				{
+					Name:     "member1",
+					Replicas: 1,
+				},
+			},
+		},
+	}
+
+	// Define the expected rb object after mutations.
+	wantRB := &workv1alpha2.ResourceBinding{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      name,
+			Namespace: namespace,
+			Labels: map[string]string{
+				workv1alpha2.ResourceBindingPermanentIDLabel: "some-unique-uuid",
+			},
+		},
+		Spec: workv1alpha2.ResourceBindingSpec{
+			Resource: workv1alpha2.ObjectReference{
+				APIVersion: "v1",
+				Kind:       "Pod",
+				Namespace:  namespace,
+				Name:       podName,
+			},
+			Clusters: []workv1alpha2.TargetCluster{
+				{
+					Name:     "member1",
+					Replicas: 1,
+				},
+			},
+		},
+	}
+
+	// Mock decoder that decodes the request into the rb object.
+	decoder := &fakeMutationDecoder{
+		obj: rb,
+	}
+
+	// Marshal the expected rb object to simulate the final mutated object.
+	wantBytes, err := json.Marshal(wantRB)
+	if err != nil {
+		t.Fatalf("Failed to marshal expected resource binding: %v", err)
+	}
+	req.Object.Raw = wantBytes
+
+	// Instantiate the mutating handler.
+	mutatingHandler := MutatingAdmission{
+		Decoder: decoder,
+	}
+
+	// Call the Handle function.
+	got := mutatingHandler.Handle(context.Background(), req)
+
+	// Check if exactly one patch is applied.
+	if len(got.Patches) != 1 {
+		t.Errorf("Handle() returned an unexpected number of patches. Expected one patch, received: %v", got.Patches)
+	}
+
+	// Verify that the only patch applied is for the UUID label.
+	// If any other patches are present, it indicates that the rb object was not handled as expected.
+	firstPatch := got.Patches[0]
+	if firstPatch.Operation != "replace" || firstPatch.Path != "/metadata/labels/resourcebinding.karmada.io~1permanent-id" {
+		t.Errorf("Handle() returned unexpected patches. Only the UUID patch was expected. Received patches: %v", got.Patches)
+	}
+
+	// Check if the admission request was allowed.
+	if !got.Allowed {
+		t.Errorf("Handle() got.Allowed = false, want true")
+	}
+}