klogr test: check vmodule support

LogSink.Enabled is sensitive to stack unwinding. logr v1.2.0  gets this wrong
by calling LogSink.Enabled at different depths for Logger.Info and
Logger.Enabled, therefore this test fails with that version.

klogr_helper_test.go

@@ -0,0 +1,35 @@
+/*
+Copyright 2023 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 klog_test
+
+import (
+	"testing"
+
+	"k8s.io/klog/v2"
+)
+
+func testVerbosity(t *testing.T, logger klog.Logger) {
+	// This runs with -v=5 -vmodule=klog_helper_test=10.
+	logger.V(11).Info("v11 not visible from klogr_helper_test.go")
+	if logger.V(11).Enabled() {
+		t.Error("V(11).Enabled() in klogr_helper_test.go should have returned false.")
+	}
+	logger.V(10).Info("v10 visible from klogr_helper_test.go")
+	if !logger.V(10).Enabled() {
+		t.Error("V(10).Enabled() in klogr_helper_test.go should have returned true.")
+	}
+}

klogr_test.go

@@ -0,0 +1,67 @@
+/*
+Copyright 2023 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 klog_test
+
+import (
+	"bytes"
+	"flag"
+	"regexp"
+	"testing"
+
+	"k8s.io/klog/v2"
+)
+
+func TestVerbosity(t *testing.T) {
+	state := klog.CaptureState()
+	defer state.Restore()
+
+	var fs flag.FlagSet
+	klog.InitFlags(&fs)
+	if err := fs.Set("v", "5"); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if err := fs.Set("vmodule", "klogr_helper_test=10"); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if err := fs.Set("logtostderr", "false"); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	var buffer bytes.Buffer
+	klog.SetOutput(&buffer)
+	logger := klog.Background()
+
+	// -v=5 is in effect here.
+	logger.V(6).Info("v6 not visible from klogr_test.go")
+	if logger.V(6).Enabled() {
+		t.Error("V(6).Enabled() in klogr_test.go should have returned false.")
+	}
+	logger.V(5).Info("v5 visible from klogr_test.go")
+	if !logger.V(5).Enabled() {
+		t.Error("V(5).Enabled() in klogr_test.go should have returned true.")
+	}
+
+	// Now test with -v=5 -vmodule=klogr_helper_test=10.
+	testVerbosity(t, logger)
+
+	klog.Flush()
+	expected := `^.*v5 visible from klogr_test.go.*
+.*v10 visible from klogr_helper_test.go.*
+`
+	if !regexp.MustCompile(expected).Match(buffer.Bytes()) {
+		t.Errorf("Output did not match regular expression.\nOutput:\n%s\n\nRegular expression:\n%s\n", buffer.String(), expected)
+	}
+}