Add new dynamic fake that supports server-side apply / field managers

client/fake/README.md

@@ -0,0 +1,149 @@
+# Fake Dynamic Client
+
+Enhanced fake dynamic client for testing Kubernetes controllers with Custom Resource Definitions (CRDs).
+
+## Features
+
+- **Server-Side Apply**: Full field management and strategic merge patch support
+- **CRD Support**: Automatic registration and schema validation
+- **Multi-Version CRDs**: Support for CRDs with multiple API versions
+- **Embedded CRDs**: Load CRDs from `go:embed` byte data
+- **Flexible API**: Functional options for easy configuration
+
+## Quick Start
+
+### Basic Usage
+
+```go
+import "github.com/authzed/controller-idioms/client/fake"
+
+// Basic client
+client := fake.NewClient(scheme)
+
+// With CRDs and initial objects
+client := fake.NewClient(scheme,
+    fake.WithCRDs(crd1, crd2),
+    fake.WithObjects(existingObject),
+)
+
+// With embedded CRD files
+client := fake.NewClient(scheme,
+    fake.WithCRDBytes(embeddedCRDs1, embeddedCRDs2),
+)
+```
+
+### Using go:embed
+
+```go
+//go:embed testdata/my-crds.yaml
+var embeddedCRDs []byte
+
+func TestMyController(t *testing.T) {
+    client := fake.NewClient(scheme, fake.WithCRDBytes(embeddedCRDs))
+
+    // Create custom resources
+    myResource := &unstructured.Unstructured{
+        Object: map[string]interface{}{
+            "apiVersion": "example.com/v1",
+            "kind":       "MyResource",
+            "metadata":   map[string]interface{}{"name": "test"},
+            "spec":       map[string]interface{}{"replicas": 3},
+        },
+    }
+
+    gvr := schema.GroupVersionResource{
+        Group: "example.com", Version: "v1", Resource: "myresources",
+    }
+
+    created, err := client.Resource(gvr).Namespace("default").Create(
+        context.TODO(), myResource, metav1.CreateOptions{},
+    )
+    // Test your controller logic...
+}
+```
+
+## API Reference
+
+### NewClient (Recommended)
+
+```go
+func NewClient(scheme *runtime.Scheme, opts ...ClientOption) dynamic.Interface
+```
+
+Main constructor with functional options:
+
+- `WithCRDs(crds...)` - Add CRD objects
+- `WithCRDBytes(data...)` - Add CRDs from YAML/JSON bytes
+- `WithCustomGVRMappings(mappings)` - Custom GVR to ListKind mappings
+- `WithOpenAPISpec(path)` - Custom OpenAPI spec file
+- `WithObjects(objects...)` - Initial objects in the client
+
+### Other Constructors
+
+These constructors are provided to mirror the upstream dynamic client interface,
+but they are less flexible than `NewClient`:
+
+```go
+func NewFakeDynamicClient(scheme *runtime.Scheme, objects ...runtime.Object) dynamic.Interface
+func NewFakeDynamicClientWithCustomListKinds(scheme *runtime.Scheme, gvrToListKind map[schema.GroupVersionResource]string, objects ...runtime.Object) dynamic.Interface
+```
+
+## CRD Format
+
+Supports YAML and JSON, single or multi-document:
+
+```yaml
+---
+apiVersion: apiextensions.k8s.io/v1
+kind: CustomResourceDefinition
+metadata:
+  name: widgets.example.com
+spec:
+  group: example.com
+  names:
+    kind: Widget
+    plural: widgets
+  # ... rest of CRD spec
+---
+apiVersion: apiextensions.k8s.io/v1
+kind: CustomResourceDefinition
+metadata:
+  name: gadgets.example.com
+# ... second CRD
+```
+
+## Examples
+
+### Multiple CRD Sources
+
+```go
+client := fake.NewClient(scheme,
+    fake.WithCRDs(parsedCRD),                    // From CRD objects
+    fake.WithCRDBytes(widgetCRDs, gadgetCRDs),   // From embedded bytes
+    fake.WithObjects(existingResources...),      // Pre-existing objects
+)
+```
+
+### Server-Side Apply
+
+```go
+applied, err := client.Resource(gvr).Namespace("default").Apply(
+    context.TODO(), "resource-name", resource,
+    metav1.ApplyOptions{
+        FieldManager: "my-controller",
+        Force:        true,
+    },
+)
+```
+
+### Multi-Version CRDs
+
+```go
+// Different versions of the same resource
+v1alpha1GVR := schema.GroupVersionResource{Group: "example.com", Version: "v1alpha1", Resource: "apps"}
+v1GVR := schema.GroupVersionResource{Group: "example.com", Version: "v1", Resource: "apps"}
+
+// Both work independently
+client.Resource(v1alpha1GVR).Create(...)
+client.Resource(v1GVR).Create(...)
+```