Add tests for resourcevalidation plugin

Signed-off-by: James Munnelly <jmunnelly@apple.com>

internal/plugin/admission/resourcevalidation/BUILD.bazel

@@ -1,8 +1,8 @@
-load("@io_bazel_rules_go//go:def.bzl", "go_library")
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
 
 go_library(
     name = "go_default_library",
-    srcs = ["plugin.go"],
+    srcs = ["resourcevalidation.go"],
     importpath = "github.com/jetstack/cert-manager/internal/plugin/admission/resourcevalidation",
     visibility = ["//:__subpackages__"],
     deps = [
@@ -31,3 +31,16 @@ filegroup(
     tags = ["automanaged"],
     visibility = ["//visibility:public"],
 )
+
+go_test(
+    name = "go_default_test",
+    srcs = ["resourcevalidation_test.go"],
+    embed = [":go_default_library"],
+    deps = [
+        "@io_k8s_api//admission/v1:go_default_library",
+        "@io_k8s_apimachinery//pkg/apis/meta/v1:go_default_library",
+        "@io_k8s_apimachinery//pkg/runtime:go_default_library",
+        "@io_k8s_apimachinery//pkg/runtime/schema:go_default_library",
+        "@io_k8s_apimachinery//pkg/util/validation/field:go_default_library",
+    ],
+)

internal/plugin/admission/resourcevalidation/resourcevalidation.go

@@ -35,6 +35,8 @@ const PluginName = "ResourceValidation"
 
 type resourceValidation struct {
 	*admission.Handler
+
+	validationMappings map[schema.GroupVersionResource]validationPair
 }
 
 // Register registers a plugin

internal/plugin/admission/resourcevalidation/resourcevalidation_test.go

@@ -0,0 +1,104 @@
+/*
+Copyright 2021 The cert-manager 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 resourcevalidation
+
+import (
+	"context"
+	"reflect"
+	"testing"
+
+	admissionv1 "k8s.io/api/admission/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/runtime/schema"
+	"k8s.io/apimachinery/pkg/util/validation/field"
+)
+
+var (
+	sampleSchemaGVR = schema.GroupVersionResource{
+		Group:    "sample-group",
+		Version:  "sample-version",
+		Resource: "sample-resource",
+	}
+	sampleMetaGVR = metav1.GroupVersionResource{
+		Group:    sampleSchemaGVR.Group,
+		Version:  sampleSchemaGVR.Version,
+		Resource: sampleSchemaGVR.Resource,
+	}
+
+	alwaysFailsCreateFunc = func(a *admissionv1.AdmissionRequest, obj runtime.Object) (field.ErrorList, []string) {
+		panic("create function not expected to be called")
+	}
+	alwaysFailsUpdateFunc = func(a *admissionv1.AdmissionRequest, oldObj, obj runtime.Object) (field.ErrorList, []string) {
+		panic("update function not expected to be called")
+	}
+
+	alwaysFailsValidationPair = validationPair{
+		create: alwaysFailsCreateFunc,
+		update: alwaysFailsUpdateFunc,
+	}
+)
+
+func TestResourceValidation(t *testing.T) {
+	tests := map[string]struct {
+		mapping     map[schema.GroupVersionResource]validationPair
+		req         admissionv1.AdmissionRequest
+		oldObj, obj runtime.Object
+
+		expectedWarnings []string
+		expectedError    error
+	}{
+		"should not perform any validation if no validation functions are registered": {
+			mapping: map[schema.GroupVersionResource]validationPair{},
+			req: admissionv1.AdmissionRequest{
+				Operation:       admissionv1.Create,
+				RequestResource: &sampleMetaGVR,
+			},
+		},
+		"does nothing for non-create or update operations": {
+			mapping: map[schema.GroupVersionResource]validationPair{
+				sampleSchemaGVR: alwaysFailsValidationPair,
+			},
+			req: admissionv1.AdmissionRequest{
+				Operation:       admissionv1.Connect,
+				RequestResource: &sampleMetaGVR,
+			},
+		},
+	}
+	for name, test := range tests {
+		t.Run(name, func(t *testing.T) {
+			p := NewPlugin().(*resourceValidation)
+			p.validationMappings = test.mapping
+			warnings, err := p.Validate(context.Background(), test.req, test.oldObj, test.obj)
+			compareErrors(t, test.expectedError, err)
+			if !reflect.DeepEqual(test.expectedWarnings, warnings) {
+				t.Errorf("unexpected warnings. exp=%v, got=%v", test.expectedWarnings, warnings)
+			}
+		})
+	}
+}
+
+func compareErrors(t *testing.T, exp, act error) {
+	if exp == nil && act == nil {
+		return
+	}
+	if exp == nil && act != nil ||
+		exp != nil && act == nil ||
+		exp.Error() != act.Error() {
+		t.Errorf("error not as expected. exp=%v, act=%v", exp, act)
+	}
+}