client-go/test: warning handler with contextual logging

The default handler now uses contextual logging. Instead of

     warnings.go:106] warning 1

it now logs the caller of client-go and uses structured, contextual
logging

     main.go:100] "Warning" message="warning 1"

Users of client-go have the choice whether the handler that they provide uses
the traditional API (no API break!) or contextual logging.

Kubernetes-commit: 48fb886325fce4b16e4067caadb7bcd3044d460f

rest/warnings_test.go

@@ -0,0 +1,57 @@
+/*
+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 rest
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDefaultWarningHandler(t *testing.T) {
+	t.Run("default", func(t *testing.T) {
+		assert.IsType(t, WarningHandlerWithContext(WarningLogger{}), getDefaultWarningHandler())
+	})
+
+	deferRestore := func(t *testing.T) {
+		handler := getDefaultWarningHandler()
+		t.Cleanup(func() {
+			SetDefaultWarningHandlerWithContext(handler)
+		})
+	}
+
+	t.Run("no-context", func(t *testing.T) {
+		deferRestore(t)
+		handler := &fakeWarningHandlerWithLogging{}
+		//nolint:logcheck
+		SetDefaultWarningHandler(handler)
+		getDefaultWarningHandler().HandleWarningHeaderWithContext(context.Background(), 0, "", "message")
+		assert.Equal(t, []string{"message"}, handler.messages)
+		SetDefaultWarningHandler(nil)
+		assert.Nil(t, getDefaultWarningHandler())
+	})
+
+	t.Run("with-context", func(t *testing.T) {
+		deferRestore(t)
+		handler := &fakeWarningHandlerWithContext{}
+		SetDefaultWarningHandlerWithContext(handler)
+		assert.Equal(t, handler, getDefaultWarningHandler())
+		SetDefaultWarningHandlerWithContext(nil)
+		assert.Nil(t, getDefaultWarningHandler())
+	})
+}