testenv: Allow klog and glog to coexist

This change allows test environments with glog to work with testenv.

Signed-off-by: Sunny <darkowlzz@protonmail.com>

runtime/testenv/testenv.go

@@ -25,6 +25,7 @@ package testenv
 
 import (
 	"context"
+	"flag"
 	"fmt"
 	"sync"
 	"time"
@@ -53,7 +54,19 @@ var (
 )
 
 func init() {
-	klog.InitFlags(nil)
+	// NOTE: The following enables glog and klog to coexist. If a test depends
+	// on a package that uses glog, klog flag initialization here would result
+	// in redeclaration of some flags. The following creates a new FlagSet and
+	// uses it to initialize klog.
+	// Refer: https://github.com/kubernetes/klog/blob/f8e668dbaa5f6f0e6a5c24ffd7667263840d79ae/examples/coexist_glog/coexist_glog.go
+	// The klog flags set belog are not available to the klogr logger below
+	// because they aren't set on the global flagset. To prevent conflicting
+	// with any flags registered later during the test setup, the flags are left
+	// empty. In the tests, a custom logger can be created with all the
+	// necessary flags and assigned to the logger explicitly.
+	klogFlags := flag.NewFlagSet("klog", flag.ExitOnError)
+	klog.InitFlags(klogFlags)
+
 	logger := klogr.New()
 	log.SetLogger(logger)
 	ctrl.SetLogger(logger)