feature(dra): add mock workqueue for controller unit test

staging/src/k8s.io/dynamic-resource-allocation/controller/mock_queue_test.go

@@ -0,0 +1,165 @@
+/*
+Copyright 2024 The Kubernetes 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 controller
+
+import (
+	"slices"
+	"time"
+
+	"k8s.io/client-go/util/workqueue"
+)
+
+// TODO (pohly): move this to k8s.io/client-go/util/workqueue/workqueue.go
+// if it turns out to be generally useful. Doc comments are already written
+// as if the code was there.
+
+// MockQueue is an implementation of [TypedRateLimitingInterface] which
+// can be used to test a function which pulls work items out of a queue
+// and processes them.
+//
+// A null instance is directly usable. The usual usage is:
+//
+//	var m workqueue.Mock[string]
+//	m.SyncOne("some-item", func(queue workqueue.TypedRateLimitingInterface[string]) { ... } )
+//	if diff := cmp.Diff(workqueue.Mock[string]{}, m); diff != "" {
+//	    t.Errorf("unexpected state of mock work queue after sync (-want, +got):\n%s", diff)
+//	}
+//
+// All slices get reset to nil when they become empty, so there are no spurious
+// differences because of the nil vs. empty slice.
+type Mock[T comparable] struct {
+	// Ready contains the items which are ready for processing.
+	Ready []T
+
+	// InFlight contains the items which are currently being processed (= Get
+	// was called, Done not yet).
+	InFlight []T
+
+	// MismatchedDone contains the items for which Done was called without
+	// a matching Get.
+	MismatchedDone []T
+
+	// Later contains the items which are meant to be added to the queue after
+	// a certain delay (= AddAfter was called for them).
+	Later []MockDelayedItem[T]
+
+	// Failures contains the items and their retry count which failed to be
+	// processed (AddRateLimited called at least once, Forget not yet).
+	// The retry count is always larger than zero.
+	Failures map[T]int
+
+	// ShutDownCalled tracks how often ShutDown got called.
+	ShutDownCalled int
+
+	// ShutDownWithDrainCalled tracks how often ShutDownWithDrain got called.
+	ShutDownWithDrainCalled int
+}
+
+// MockDelayedItem is an item which was queue for later processing.
+type MockDelayedItem[T comparable] struct {
+	Item     T
+	Duration time.Duration
+}
+
+// SyncOne adds the item to the work queue and calls sync.
+// That sync function can pull one or more items from the work
+// queue until the queue is empty. Then it is told that the queue
+// is shutting down, which must cause it to return.
+//
+// The test can then retrieve the state of the queue to check the result.
+func (m *Mock[T]) SyncOne(item T, sync func(workqueue.TypedRateLimitingInterface[T])) {
+	m.Ready = append(m.Ready, item)
+	sync(m)
+}
+
+// Add implements [TypedInterface].
+func (m *Mock[T]) Add(item T) {
+	m.Ready = append(m.Ready, item)
+}
+
+// Len implements [TypedInterface].
+func (m *Mock[T]) Len() int {
+	return len(m.Ready)
+}
+
+// Get implements [TypedInterface].
+func (m *Mock[T]) Get() (item T, shutdown bool) {
+	if len(m.Ready) == 0 {
+		shutdown = true
+		return
+	}
+	item = m.Ready[0]
+	m.Ready = m.Ready[1:]
+	if len(m.Ready) == 0 {
+		m.Ready = nil
+	}
+	m.InFlight = append(m.InFlight, item)
+	return item, false
+}
+
+// Done implements [TypedInterface].
+func (m *Mock[T]) Done(item T) {
+	index := slices.Index(m.InFlight, item)
+	if index < 0 {
+		m.MismatchedDone = append(m.MismatchedDone, item)
+	}
+	m.InFlight = slices.Delete(m.InFlight, index, index+1)
+	if len(m.InFlight) == 0 {
+		m.InFlight = nil
+	}
+}
+
+// ShutDown implements [TypedInterface].
+func (m *Mock[T]) ShutDown() {
+	m.ShutDownCalled++
+}
+
+// ShutDownWithDrain implements [TypedInterface].
+func (m *Mock[T]) ShutDownWithDrain() {
+	m.ShutDownWithDrainCalled++
+}
+
+// ShuttingDown implements [TypedInterface].
+func (m *Mock[T]) ShuttingDown() bool {
+	return m.ShutDownCalled > 0 || m.ShutDownWithDrainCalled > 0
+}
+
+// AddAfter implements [TypedDelayingInterface.AddAfter]
+func (m *Mock[T]) AddAfter(item T, duration time.Duration) {
+	m.Later = append(m.Later, MockDelayedItem[T]{Item: item, Duration: duration})
+}
+
+// AddRateLimited implements [TypedRateLimitingInterface.AddRateLimited].
+func (m *Mock[T]) AddRateLimited(item T) {
+	if m.Failures == nil {
+		m.Failures = make(map[T]int)
+	}
+	m.Failures[item]++
+}
+
+// Forget implements [TypedRateLimitingInterface.Forget].
+func (m *Mock[T]) Forget(item T) {
+	if m.Failures == nil {
+		return
+	}
+	delete(m.Failures, item)
+}
+
+// NumRequeues implements [TypedRateLimitingInterface.NumRequeues].
+func (m *Mock[T]) NumRequeues(item T) int {
+	return m.Failures[item]
+}